Fig. 165 shows a portion of the north-west ramparts of the city of Carcassonne, with the first round tower; to the left of the drawing is the Romano-Visigothic tower, flanking right and left the curtains of the same period. [Illustration: 165. CITY OF CARCASSONNE. NORTH-WEST RAMPARTS. ROMANO-VISIGOTHIC TOWER (FIRST ON THE LEFT)] In accordance with the Roman tradition the _enceinte_ of a town, formed, as we have seen, of ramparts strengthened by towers, were further defended by a citadel or keep, of which we shall have more to say in the following chapter. This keep commanded the whole place, which was usually situated on the slope of a hill above the bank of a river. The bridge which communicated with the opposite bank was fortified by a gate-house or _tête de pont_, to guard the passage. The circumvallation of towns often consisted of a double enclosure, divided by a moat. By the close of the twelfth century architects had caught the inspiration of the great military works of the Crusaders in the East, and military architecture had progressed on the same lines as religious and monastic architecture. The territories, conquered by the Crusaders in the course of establishing the Christian supremacy in the East, had been divided into feofs as early as the twelfth century. These soon boasted castles, churches, and monastic foundations, of the Cistercian and Premonstrant orders among others. According to G. Rey, the following abbeys and priories were built in the neighbourhood of Jerusalem at this period:--The monasteries of Mount Sion, Mount Olivet, Jehoshaphat, St. Habakkuk, and St. Samuel, etc., and in Galilee, those of Mount Tabor and Palmarée. The military organisation was regulated by the _Assises de la haute Cour_ (Assizes of the Supreme Court), which determined the number of knights to be furnished by each feof for the defence of the kingdom, and in like manner, the number of men-at-arms required from each church and each community of citizens.... The middle of the twelfth century was the period at which the Christian colonies of the Holy Land were most flourishing. Undeterred by the wars of which Syria was the theatre, the Franks had promptly assimilated the Greek and Roman tradition as manifested in Byzantine types of military architecture. The double enclosure flanked by towers, one of the main features of Syrian fortresses built by the Crusaders, was borrowed from the Greeks. Many of their strongholds, notably Morgat, the so-called _Krak_ of the knights, and Tortosa, were of colossal proportions. They may be divided into two classes. In the first, the buildings are of the Frankish type, and seem to be modelled on the French castles of the eleventh and twelfth centuries. The flanking towers are nearly always round; they contain a defensive story, while their summits and those of the intervening curtains are crowned with battlements in the French fashion. Other features subsequently introduced were: the double