Palaeochristian architecture

The architecture early Christian, also called architecture early Christian, is one that was built between the late third century -under the mandate of Constantine the Great – until the sixth century epoch of Emperor Justinian I. He was born primarily to meet the need for building structures of his own for the Christian religion.

Although it originated in Syria and Egypt, it quickly passed to the West, and went to Rome – the center of Christianity – where the first manifestations of architecture monuments, in the field of cemeteries or catacombs took place ; It was a stage of secrecy due to the persecutions that were object those who practiced the Christian religion. At this same time, to celebrate religious worship assemblies, private homes were used, adapting some of their rooms for these purposes (domus ecclesiae).

The following stage begins in 313 with the Edict of Milan, promulgated by the emperors Constantine the Great – after its conversion – and Licini I, according to which Christians were granted full rights to public manifestation of their beliefs :

«We, Augusts Constantine and Licini (…) have judged that, among all that we saw agreed upon for the universal good, we should prefer to deal with what affects the divine honor, and give Christians the same as all others, the free faculty of professing the religion that each one wanted (…)

From this legalization of the Christian religion three new architectural models will appear, although in fact it was reinterpretations of previous structures: basilicas, baptistries and mausoleums. These two last buildings mostly adopted the centralized, circular or polygonal plant, which was more suited to the complex function they were intended for. What most stood out, however, was the emergence of the basilicas, adapting the Roman building of the same name; The role, however, went from being civil to being religious. The main reason for the Paleo-Christian basilica is to achieve the desired architectural space, by covering what formed the porchColumned by two Greek Stoà faces; this happened if they came from the Greek temple model, although it is thought that its architectural typology derives from the Roman temple. The temples were considered both for the Greek religion and the Roman residence of God, and the function was not to be a place of prayer for the citizens: the sacrifices were made out, which is why the altar was usually in front of the church. Building and this one, since it did not have to accommodate many people, could have smaller interior stays than in the Christian case. Bruno Zevi described it like this:

«If we compare a Roman basilica and one of the new Christian churches we find, relatively, few differentiating elements apart from the stairs. »
– Bruno Zevi, art critic
There has been no clear conclusion about when and how Palaeochristian art began, both in architecture and painting, and how models could be spread from one place to another.

Historical context
The Roman Empire presented towards the III century an economic decline and great political instability: paganism, as a religion, did not provide neither the necessary consolation nor a safe salvation. The emergence of new monotheistic religions from the East – such as Judaism and its branch of Christianity, in which a God died and resurrected to achieve the salvation of all human beings – seemed to be able to fill the new spiritual needs in this time of uncertainty. The Christianity was being introduced gradually through the preaching of the gospel that men like PaulThey performed throughout the empire. The rites of this Christian religion were much simpler and closer to the people of the people than the great ceremonies and pomposity with which the official cult of paganism was celebrated. During the first century after the death of Christ, the number of believers evolved slowly; Rites were common prayer, baptism and funerary offerings or banquets. Towards the middle of the 3rd century it had about fifty thousand believers and in Asia Minor more than half were already Christians.

A legend explains the conversion to the Christianity of Constantine the Great : before the battle of the Pont Milvi he had a vision of a cross in flames with the inscription “With this sign, you will conquer”. Constantine came out victorious and the monogram of the Cross became her symbol. In 313, through the Edict of Milan, he legitimized Christianity and was considered the head of the Church – Maxim Pontifex -; made important donations, supported the construction of temples and summoned the first Council of Nicea – and the first ecumenical council – in 325 in Nicea of Bitinia, a city of Asia Minor. In 330 he moved the headquarters of the Roman Empire to Byzantium, a city that changed its name to Constantinople, and dedicated it to the Virgin Mary. This move had the subsequent effect, in 395, of dividing the kingdom into the Eastern Roman Empire – or the Byzantine Empire – and the Roman Empire of the West. Emperor Theodosius I, at the end of the fourth century, was able to make the Christian religion official with the Edict of Thessalonica, and the number of believers in Paganism was increasingly reduced. The Barbarian Invasionsof century I SAW ended the paleo-christian architecture to the Empire of the West; The territories of Syria, Egypt and North Africa marked the limit until the Arab conquest (around the 7th century).

The Byzantine architecture produced a new language from the sixth century, which begins at the time of the Emperor Justinian I and marks a break with the early Christian architecture of the West; Byzantine architects reclaim the structure covered with dome and the concept of the central plant, such as the church of Santa Sofia de Constantinople, the basilica of San Vidal de Ravenna and, in this same town, the basilica of Saint Apol • Linar el Nou, which still has the type of Paleo-Christian basilica church rectangular with three longitudinal ships and the entrance hall.

The catacombs were subterranean places that, after the death of Christ, the first Christians used to bury their dead, although there were also underground galleries that were used by people belonging to the Jewish religion and paganism. They were located outside the walls of the city, since the Roman law of the Empire did not allow burials within the urban area for religious and hygiene reasons. Although they are found in many cities, the largest and most extensive catacombs are those of Rome, which in total sum about sixty different, with about 750,000 tombs; Its total length is between 150 and 170 kilometers. It is believed that the builders of the catacombs took advantage of the old abandoned galleries, from which a stone called Puzolana had been extracted, which once crushed it was used to make cement. Studies conducted in the 19th century under the direction of the Jesuit Marchi and his student, the archeologist Juan Bautista Rossi, lowered the theory that the galleries had been used previously to extract the Puchanan stone and gave as true the one that He postulated that the galleries were specifically excavated for use as a cemetery. The organization and construction of the first cemetery is attributed to Pope Calixt I and the approximate date according to Paul Styger’s study for the catacomb of Saint Calixtus, in the year 200, agrees with this attribution. The use of the catacombs was prolonged, due to the custom of the faithful, even after the Edict of Milan, abandoning itself after the pillage of Rome in 410, partly because of the insecurity that was felt outside the city; The main reason, however, was that at that time there were already large and numerous basilicas that could be used for funeral services and to keep the relics of the martyrs.

The majority of the catacombs realized in Rome had their origin in Century II; Most of them are buried along the great roads at the exit of the city such as Via Àpia, Via Ardeatina, Via Salaria or Via Nomentana. They consist of a system of underground galleries that form a kind of maze. For its construction, a first level was first excavated, and it was descending to lower floors following the irregular lines of the ground; It was possible to get to deepen until thirty meters. On the walls, the gaps were dug for the tombs horizontally (loculi), normally to contain a single corpse, although exceptionally they could contain more bodies; They were closed with a stone slab or brick, which often had inscriptions in Latin or Greek. There was another type of tomb destined to more important personages called arcosoli that consisted of a niche covered by an arc and locked up with a slab. The cubicle was the space that contained the various loculi of the same family, and also contained, apart from the tombs, small chapels decorated with frescoes. At the junctions of the galleries there were small crypts that contained the tomb of a martyr. In almost all the catacombs there are open skylights on the roof of the crypts or at the galleries; They were used, first of all, to raise the surface of the earth from the excavations and, once the construction was finished, they were left open to serve as points of light and ventilation.

Symbolism and iconography
The symbols were a dominant theme in the catacombs: in almost all the graves were images with some symbols, such as the dove representing peace, the cross and the anchor representing salvation, the phoenix representing the resurrection and the fish and the Good Shepherd corresponding to the image of Christ. The fresco paintings reproduced scenes from the Old Testament, such as the sacrifice of Isaac, Noah and his ark, Daniel in the grave with lions, Elijah in his car or the three Hebrews (Ananies, Misael and Azaries) at burning oven There are also numerous New Testament storiesabout the life of Christ and representations of the Virgin Mary with the Infant sitting on her skirt (the so-called Theotokos). Many of these images are represented for the first time in the catacombs of Priscilla in Rome.

Domus ecclesiae
The Domus Ecclesiae (Latin word which means “house of assembly” or “house church”) was a private building for the early Christians adapted to the needs of worship. One of the oldest Christian churches is in the city of Dura Europos, an ancient Hellenistic settlement converted into a Roman border garrison, located near the Euphrates River, in present-day Syria.

This site was excavated in 1930 and between its buildings was a structure that had been transformed for use as a church, which could date from year 232 thanks to a graphite. Beside him, a room that was used as a baptistry had been decorated and decorated; Some of its frescoes, which represent the Good Shepherd, the healing of the paralytic and Adam and Eve or Christ walking on the water, are also treated in the catacombs.

The first meeting rooms of the Christian communities in Rome were carried out in private houses known as titulus (plural tituli). Normally the triclini, the largest room, was adapted for the celebration of his religious rites. These rites or ceremonies included prayers, reading passages of the Gospels and Epistles as well as sermons; In the 3rd century, the presidency of the Mass had episkopoi (bishops). There was a separation between bishops and catechums, those who were receiving training but had not yet received baptism: they were required to go to another room when the time came to celebrate the Eucharist. Before the construction of churches or basilicas the altar did not exist, but simply a table to celebrate the cult.

Ten meters below the current basilica of San Martino ai Monti is one of the private houses of Rome used as domus ecclesiae : it is identified as Titulus Aequitii and its owner was Equitius. It was built at the end of the second century or beginning of the third century and it was a rectangular building with two floors with a large central courtyard. The ground floor is believed to be the one that was intended for the functions of worship: it consisted of a large room divided into columns where the Eucharist was celebrated and another room reserved for catechumens, although no archaeological remains of the presence of a baptismal font. The upper floor should have been used as a private home. After the Edict of Milan, the titles could be transformed, thanks to the donation of their owners and owners, in churches. The first church of Titulus Aequitii was founded by Pope Silvestre I in the 4th century: in its origin it was dedicated to all martyrs. Subsequently, at the turn of the 5th and 6th centuries, the pope Símmac I raised a new one on the previous one, the largest, and dedicated it to Saint Martí de Tours and to Pope San Silvestre. In the 9th century, Pope Sergi II ordered his restoration and construction of the current basilica of San Martino ai Monti.

Thanks to the proclamation of the Edict of Milan, Christians were free to practice their religious cults: they built basilicas following the model that served the Romans as civil centers – with market activities – and as courtroom Those of new construction followed the same models and only they differentiated in their use: the Christians realized the cult and the assemblies inside, whereas the greco-Roman cult was carried out around the temple.

With Constantine converted to Christianity, his leaders – pope, bishops and clergy in general – occupied positions within Roman society as carriers of the new state religion. At the same time, the Christian architecture went from the simple refuge in private houses to new monumental forms inspired by the Roman architecture, with the necessary changes when the buildings were taken advantage of from previous Roman constructions, for its application to the new ones functions of religion cults: altar for the celebration of the mass, nártex for the catechumens, etc. The new religion needed more places of worship and increasingly greater, since, day by day, its number of believers increased. In spite of the great amount of Christian temples or basilicas that were constructed during century IV, few subsisted, since, during the later centuries many of them were destroyed or reformed.

In general, the Paleo-Christian basilica consisted of three parts:

The atrium (or narthex) of access in front of the door of the basilica, occupied by the non- baptized. He used to have a large pile of water for ablutions.
The longitudinal body, divided into three or five ships separated by columns. The central nave used to be taller and the side naves sometimes had over galleries or stands called ” matroneu”, specially made for women.
The headboard, which was occupied by an apse covered with a fourth dome dome ; In the presbytery the altar was placed.
The cover of the primitive paleochristian basilica used to be on two sides with the armored armored door frames, which were so heavy, so that their walls, without the need for buttresses, were completely smooth. The exterior light came from large windows open to the outer walls of the side naves and, when the central nave was higher than the others, the claristory. Many of the materials used in new constructions, such as columns and capitals, were seized from earlier Roman buildings.

The Palaeochristian architecture, like the Roman civil basilica, and unlike the Roman and Greek temples with its peristiles, used closed construction, since the old models were rejected because of their significance contrary to Christianity. In addition, the Roman and Greek stylistic types were not easy to adjust to the new Christian rite; for example, the pagan sacrifice was realized in an altar located to the outside of the temple and to the cell the statue of the God placed itself. The Christian religion, on the other hand, needed an altar to carry out the act of symbolic sacrifice, the transubstantiationof wine and bread in the blood and body of Christ; this act had always been carried out in closed places, as in the Holy Supper celebrated by Christ. In the 4th century, for the ritual, a path was needed for the procession of the clergy, a part where the altar was placed and the mass was celebrated, another part for the faithful who participated in the procession and communion and another for the catechumenes or not baptized.

Constantinian Basílics

Basilica of Constantine de Trèveris
The Christian basilica, then, was used only for a single ritual, unlike the Roman civil basilica, which had had various public services. One of the models that was thought to have been most used during the origins of the Christian basilica is the civil basilica of Constantí de Trèveris, built in 310, with a rectangular space and a large semicircular apse that housed the throne of the emperor Roman It was built with the stones of older buildings, and it was not an isolated building, but at the time of late AntiquityIt was part of the enclosure of the imperial palace: the vestiges of adjacent buildings were discovered in the eighties and today they are visible. Some traces of the plaster covering the bricks of origin, as well as some old features, were kept at the height of the window openings.

Basilica of St. John Lateran
In the first Christian basilicas, this functionality cited in the previous section was very taken into account. One of the first donations of Emperor Constantine to the bishop of Rome – surely the pope Melquíades I – was 313 and served to build his residence, the Lateran palace. The basilica dedicated to San Salvador (the present basilica of San Juan del Laterano), consecrated by Pope Silvestre I. Over time this basilica has been transformed, but one can know what the original project was like: it consisted of a larger central nave and two narrower ones on each side separated by large columns; The central nave was taller and had a two-seater roof. Between this cover and those of the side naves there was the claristorium, a whole row of windows that illuminated the interior of the basilica. All the construction was made of brick, except the marble columns and the wooden deck. The bishop of Rome, followed by his clergy, entered the procession by the central nave until he reached the great apse, where they had their seats and the altar to celebrate the ceremony. Meanwhile, the faithfulthey used the closest side naves to the central and the catechumens, the outer spaces that, apparently, were separated by curtains placed in the intercolumns that would run during certain acts of the ritual.

Old basilica of Saint Peter
Also in Rome, under the patronage of Constantí, the construction of the old basilica of San Pedro, between 326 and 330, began, which would become one of the most important Paleo-Christian basilicas. It was realized on where was the grave of the saint, on the Vatican hill, and where there was already a small sanctuary in his honor. The exact chronology of the construction is not known, although the Liber Pontificalis indicates that it was built by Constantine during the pontificate of Pope Silvestre I (314-335). Currently disappeared under later constructions, the old basilica of San Pedro is known thanks to documents prior to its total demolition during the Renaissance. Several writers left detailed descriptions, such as Tiberius Alfarano in De Basilicae Vaticanae antiquissima et nova structura (1582), with designs from the former basilica’s floor – the work was not published until 1914- or Onofrio Panvinio in De rebus Antigua memorabilibus you praestantia basilicae S. Petri Apostolorum libri septem.

The basilica had a very wide structure, with one hundred and ten meters in length and five ships – the central double-width one that the sides-, divided each by twenty-one marble columns. It was illuminated in the same way that the one of San Juan del Laterano, with a large portal of three doors to an atrium; In the inner wall of it five doors were opened, one for each ship. At the crossroads, before the altar, was the martyrium of St. Peter, with its relics, under a marble canopy supported on four columns, also of marble, where pilgrims met.

Basilica of Sant Pau Extramurs
During these same years, Constantine promoted the construction of the Basilica of Sant Pau Extramuros on the tomb of Saint Paul, who was buried, after having undergone martyrdom, in a large necropolis that occupied the entire area of the basilica and of the surrounding area; on his tomb in the Via Ostiense, they built an shrines – eyebrow memory. On this site, and due to the difficulties of the land, the construction of the basilica was a little smaller than that of the apostle Saint Peter: it only had three ships, although this was rectified in 386 by changing them the orientation and building a much larger church with five ships and with a cruise; But the altar was left on the tomb of the saint, as was customary. The Pope Sirici I consecrated the building. Finally, this basilica was destroyed during a fire in 1823, and only the apse, the altar and the crypt where the remains of St. Paul were found were saved.

Basilica of Santa Agnès Extramurs
The basilica of Santa Agnès Extramuros was built in 324 on the catacombs of Via Nomentana, where the saint was buried. It is much smaller than that of San Pedro and San Pablo and is semi-suburban. It has three ships and at the top of the sides has the matroneo, the gallery for women; The columns of separation of the ships are made with marbles of various colors. In the apse are preserved mosaics, from a reconstruction made by Pope Honorius I in the mid-seventh century, which are represented three isolated figures: in the center of St. Agnes, and their sides, popes Simmaco I and Honorius I. They are facing a golden background, a typical example of the Byzantine influence in this Palaeo-Christian age.

Basics in the Holy Land
Constantine also contributed to the construction of other churches in the Holy Land : in the city of Bethlehem, that of the Nativity, commemorating the birth of Jesus, and in Jerusalem the Holy Sepulcher, to honor the tomb of Christ (the same emperor had given instructions to make this temple “the most beautiful basilica of the earth”).

The church of the Nativity of Bethlehem was built around 333, although it had to be reformed in the 6th century, after it was burned and destroyed during the rebellion of the Samaritans of the year 529 led by Julianus ben Sabar. It had a longitudinal plant that had a large atrium, in front of the entrance, which served as a rest for pilgrims. The basilica consisted of five ships with a practically square plant (28 x 29 meters) and, centered at the bottom, there was an octagonal opening, covered with wood and surrounded by a railing, where you could see the birthplace of Jesus.

The Basilica of the Holy Sepulcher, on the other hand, was consecrated in 335. Emperor Constantine I asked Bishop Macari to take charge of the work of the temple and, to do so, goes send to his own mother Santa Helena because they both directed the works. It was rectangular and had an atrium smaller than that of the church of the Nativity; Its interior was of central nave with other double sides on which there were some galleries. The separation of the ships took place by means of majestic marble columns with the golden capitals. To the apse, circling all its semicircle, there were twelve columns that symbolized the twelve apostles ; the outer lateral ships, those that ran along the wall of the building, lead to a long patio located behind the apse. In this courtyard it was found, covered by a canopy supported by twelve columns, the site of the Holy Sepulcher of Christ. A few years later, the same emperor or one of his sons performed around the old tomb the so-called ” Anastasis Rotonda” to celebrate the Resurrection, enlarging its construction with a new structure of 17 meters in diameter, with a cover Conically shaped wood and an ambulatoryAt the level of the ground and another half-circle superior in the form of a gallery.

Post-Constantinian Basílics
The post-Constantinian Basins are also called as the period of the “Sixth Renaissance”, to be the best known constructions under the mandate of Pope Sixt III.

Above a previous church, erected according to tradition by Pope Liberi I around 360, Pope Sixt III (432-440) ordered the construction of a church dedicated to the worship of the Virgin Mary shortly after her death, the dogma of the divine maternity was affirmed to the Council of Ephesus (431). In the Basilica of Santa Maria Major, the resurgence of the most classicistic forms was used, the Sixteenth Renaissance. It has a three-story plant and a Ionic columnada with voussoirs and smooth shafts, and the pilastersIn the area of skylights are of a more refined style than in the previous basilicas. This basilica is the one that best represented the new changes in the Palaeochristian style. Inside, one of the main works is the splendid cycle of mosaics on the life of the Virgin, dating from the fifth century and which still shows the stylistic characteristics of late Roman art.

Ten years before the rising of the basilica of Santa Maria Major began, the construction of a small basilica dedicated to Santa Sabina was begun on the Aventí hill, in which more harmonic proportions are appreciated and the elegance of various details such as the beautiful capitals of the corinthian columns reused from a temple of the goddess Juno. Following the characteristics of the Palaeochristian architecture, Santa Sabina has totally smooth walls built with bricks and without abutments, since the roof is made of wood and, therefore, heavy. The only thing that stands out on the outside is the row of half – point arched windows.

The baptistry is a building that is exempt and close to a temple, sometimes forming part of a larger complex. They are centrally located, usually octagonal, although there were also others like the circular one. Its function was the administration of baptism, so that in its center a great baptismal font was always placed, since, at that time, baptism was celebrated in adults and full immersion. They used to be covered by a dome and ornamented with mosaics and paintings.

Baptistery of St. John Lateran
Pope Sixt III (434-440) promoted the construction of works on previous buildings, as is the case with the Baptistery of St. John Lateran, built on an old circular structure of Constantine’s time (around 312), next to the Basilica of San Juan del Laterano. It is one of the best examples of centralized plants raised during the 5th century, and became a model for other baptistries. The building reconstructed by Pope Sixt III is centrally centralized with an octagonal shape surrounded by an ambulatory with eight columns of porphyry from other demolished buildings; The triforium is found on the ambulatory. Still, remains can be seen, on the double apses of the lobby, of a mosaic decorated with interlocking lamps. Pope Hilari I (461-468) performed the chapels dedicated to Saint John the Baptist and St. John the Evangelist.

Baptisteris Neonià i Arrià
These two baptistries – Neonian and Arriara – are located in the city of Ravenna, the capital of the Roman Empire in the 5th century. Both were registered by UNESCO in the list of World Heritage Sites in 1996 as part of the Paleochristian monuments of Ravenna. Of all the buildings that make up the set, it is believed that the two baptistries are the oldest.

The Neonian Baptistery is, according to the ICOMOS evaluation, “the best and most complete surviving example of a Baptistry of the early days of Christianity,” and “retains fluidity in the representation of the human figure derived from Greek-Roman art”. The same body comments in the evaluation of the Arriaria Baptist that “the iconography of mosaics, whose quality is excellent, is important because it illustrates the Blessed Trinity, a somewhat unexpected element in the art of a building It arises, since the Trinity was not accepted by this doctrine “.

One of the Baptistries, the Neonian, was destined for the Orthodox (for this reason it is also called the Orthodox Baptistry), and the other for the Arrians (also called the Arrians Baptistry); The latter was built by King Teodoric the Great at the end of the 5th century. In the year 565 after the sentence of the cult left, this structure was converted into a Catholic oratory, under the invocation of Santa Maria. The Neonian Baptist (or Orthodox) was built by Neone Bishop. Both have the octagonal plant – which was used in most baptisms of the Paleochristian art – due to its symbolismof the seven days of the week plus the day of the resurrection, thus relating the eighth number with God and the Resurrection. The baptismal font is at the center of the plant. They were built with bricks, with exterior walls almost without ornamentation and interiors with rich mosaics. The dome represents, in both buildings, a scene with the baptism of Jesus on the Jordan River by Saint John the Baptist in the center and, around them, the twelve apostles.

Mausoleum or martyrium
A mausoleum was a building of funerary type and of monumental character that was used to building on the place where a historical or heroic personage was buried. The site, associated with the figure of a martyr, took the name martyrium (plural martyr). He went to worship his relics, though sometimes it was like a cenotaph and his body was buried in another place. One of the oldest martyrs, dating to the year 200, is St. Peter’s, which is under the basilica of St. Peter of the Vatican. These buildings, inspired by the original heroine and originalHypens, were adapted to the needs of the funerary worship for Christian worship.

Santa Costanza Mausoleum
This building was erected as a mausoleum towards 350 by Constantine I the Great to house the remains of his daughter Costanza. It has a circular floor structure covered by a dome of 22.5 m supported by a drum in which windows that provide natural light in the building are opened. The center of the plant housed the sarcophagus of porphyry red Costanza, today moved to the Vatican Museums. It is surrounded by an ambulatoryformed by double columns and a second circle delimited by a thick wall in which you can find numerous niches and large windows of smaller size than those of the central dome. These circles are covered by individual annular canopy vaults decorated with original 4th century mosaics featuring scenes from the vintage, plant and animal motifs and putti.

Mausoleum of Constantine or the Church of the Holy Apostles
To make it use as its own mausoleum, Emperor Constantine built the old Apostles Church at the highest point in the city of Constantinople, next to its walls. This mausoleum was replaced by a new church at the time of Justinian I and later by a mosque in 1469, so there is now nothing left of the primitive mausoleum. The description is found in the work De Vita Constantini εἰς τὸν Βιὸν τοῦ μακαριου Κωνσταντινου Βασιλέως λόγοι τέσσαρες), a panegyric- more than a biography – by Eusebi de Cesarea. It had a Greek cross plant; The arm that corresponded to the entrance was slightly longer than the other three. In the central part, the emperor’s porphyry coffin was installed, flanked by cenotaphs or tombstones with the names of the apostles ; Constantine held the thirteenth place. It was realized with the idea of becoming a hero in which the emperor rested like a hero under the sign of the cross. Later, this position was changed: it was when in the year 356 the true relics of the apostles were taken to the church and the remains of Constantí moved to an independent mausoleum near the church. This new accommodation already corresponded to the traditional funeral approach, by offering a circular dome-shaped circular plant.

In the scheme of the original mausoleum described by the historian Crippa you can see the presence of a dome in each of the arms of the cross: thus, it would consist of four domes surrounding the dome with a height slightly smaller than that of this one. In addition, Crippa also proposes a floor with interlinked double collaterals, which gives rise to a peripheral ring or passage that surrounds the entire internal space.

Source from Wikipedia