Ribat of Soussa, Muslim invention of rib vaulting?
Background One of the defensive engineering structures the Muslims introduced was a fort- like edifice called Ribat. This building was designed to serve as a base for military intervention and a shelter against hostile invasion. It is also equipped to accommodate a good number of soldiers known as Murabitoon. These were religious devotees vowed to retire in the Ribat to worship, study and live a religious life at times of peace. At war times, these Murabitoon become first line soldiers defending the population and consequently answer the call of their Lord (Allah): "O you who believe! Endure, outdo all others in endurance, be ready, and observe your duty to Allah, in order that you may succeed." (Quran 3:200). This building spread all over the Muslim land and concentrated particularly in areas facing external threat known as Thughoor. Ibn Khaldun, for example, reported that The Aghlabit Emir Abu Ibrahim Ahmed built a total of 10,000 ribats in North Africa. With similar objectives in mind, the Aghlabit Emir of Quairawan Ziyadat Allah constructed the Ribat of Soussa in 821. The Ribat and the port of Soussa defended North Africa against external aggression and assisted in conquests, Futuhat, of Sicily. The plan The Ribat consists of a rectangular edifice surrounded by high defensive walls equipped with a number of arrow- slit openings and strengthened by three circular towers (figures 1&2). In the southern side the middle tower was converted into an entrance porch while its corner tower carried the cylindrical minaret (image above). This is an unusual shape differing from the famous North African, and Tunisian, square minaret. The choice of this form was to emphasise the dual use of the minaret as a means for Athaan ritual (prayer call), as a sea tower providing direction to ships and a watching post for troubled sea waters (Figure 4). The entrance is a narrow arched gate leading to a cross (groin) vaulted hall which is protected by an aperture pierced in the vault and accessed through the chamber above it. From this hole, boiled oil, water and heavy stones can be poured on the invader in case of a forced entry. Beyond the hall, there is a courtyard, which forms the centre of the complex, surrounded by vaulted galleries of arcades. Into these galleries doors of numerous chambers were opened. Above them another set of vaulted rooms were raised and accessed through the terraced roof of the arched galleries of the courtyard. These cells provided perfect study and living environments for residents of the Ribat. The Masjid (prayer room) occupies the first floor of the southern half of the building. It is composed of 11 aisles covered with barrel vaults and externally emphasised by the implantation of a small dome raised higher on the general roof level of the ribat (figure 5.) 
Architectural and design significance of the Ribat The major significance of the edifice appears in two main elements. The first is its spatial configuration which was later to leave its impressions on a number of Mosques including those of Soussa town e.g. the Great Mosque and the Mosque of Abu Fatata. Both mosques showed similar design features. Other mosques which were influenced by the Ribat were the mosques of Ibn Mardum and Casa de las Tornerias (Toledo 12th century) in Spain , and Masjid-I-Tarikz at Balkh. However, according to Marcais, Ribat of Soussa was itself an inspiration of Ribat of Monastir (Tunisia) built in 796 AD, some 25 years before. The other major significance is technical, which appears in the considerable use of both barrel and groin vaults constructed from stone. Although, the construction of such vaults is not a Muslim invention as they both appeared in Roman buildings. Barrel vaults were largely used in Roman depots and tunnels while examples of the cross vault are found in Christian (Roman and Byzantin) churches. However, these vaults were largely built from a consistent material made from rubble and concrete that was carried by scaffolding. The example of Soussa, as well as that of Monastir Ribat, shows a great skill and workmanship in the construction of the stone vault which appears to be assembled stone by stone in a similar manner to that of a wall (figure 6). More importantly is the use, at regular intervals, of stone arches underneath the vault to provide extra support for the vault as well as during the construction (figure 7). These arches were named by Muslims as Haniyat, with their first appearance being recorded in the mosque of Ukhaidir Palace (Iraq, circa 774-75). Later, they were reinvented in Europe under the name of ribs. There is consensus of scholars who consider that the ribs have revolutionised the way buildings were constructed. The ribs are also responsible for the spread of large size medieval churches of the Romanesque style. There is obvious resemblance between the ribs of the Ribat of Soussa and these European ribs (figures 8). Moreover, the Muslims did not stop at this type of ribbed vaulting as they introduced the cross and intersecting rib vaulting used as we have seen in Mosques of Cordoba and Bab Mardum of Toledo (see Architecture of Muslim Caliphate in North Africa). It is widely accepted that this type of rib vaulting (the Cordoban and Toledian), in addition to the pointed arch, was the main instrument for the introduction of the famous Gothic style, which spread in Europe between 13th and 16th century. 
Conclusion There are two main concluding remarks that can be drawn from the above. First, the evidence shows the important contribution of Ribat of Soussa to the development of architecture through the use of ribbed vaulting. Such a technique was not used in Europe until the 11th century, some 200 years after their use in Soussa. This is a clear indication of the continuing influence of Muslim architecture on Europe and the world atarge. Second, the ribat as a distinctive type of building was invented to defend the Muslim land from the aggressors. The successful combination of wordily duties of military training and readiness with religious duties of worship and study was undoubtedly the main ingredient behind the victory of Muslim predecessors. These ribats were abondoned long time ago, becoming in most cases derelict. In Soussa, the Ribat is well maintained probably due to the fortune it brings from foreign visitors. However, there are unfortunately shocking signs of bad treatment and disrespect which many of the visitors found offensive. The incorporation of some tasteless modern art paintings on these holy walls, especially the depiction of two naked women, is an abuse and disrespect to the Muslim heritage. In this concern, we appeal to the appropriate Tunisian authorities to intervene and restore the respect and dignity of this great historical and architectural building. 
by: FSTC Limited, Sun 23 February, 2003
 
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