CITADEL, a municipal fortress. The beginnings of the cita del are remote. At Tanis in Egypt there is a very ancient example; roughly quadrangular, it was built to command a stream and the adjacent ground. During the I2th dynasty of the first Theban empire a most formidable citadel was evolved, typified at Semneh, where a low wall of first defence rises upon a platform ; the citadel proper is a series of crenelated buttress-redoubts projecting at short intervals from a high, rectangular wall, with an additional highly fortified projection at one corner; scaling would have been impossible without fatal casualties.
Ancient Greek citadels were usually of Cyclopean construction (see CYCLOPAEAN MASONRY) but that of Tiryns (q.v.) has upper walls of brick. It contains the king's palace, a fact which does not change its role as the true municipal fortress but which points to the origin of the municipality itself. The amalgamation of several hamlets into a polis or city, very frequently depended upon the existence of an acron, or height, which might be fortified and which became a storehouse of provisions and ammunition as well as the shrine of the god, the home of the king and the refuge of the people.
Just as the acropolis of Athens or the walled hill of the temple of Solomon in Jerusalem were vital municipal influences, so the capitol was the consolidating and protecting factor in Rome. But the citadel of Roman cities in general was less important than those of Greece. In strong countries not contiguous upon others of the same status citadels are rare because they are unnecessary. The Roman castella covered Europe and a part of Asia and Africa at one time ; they were military centres around which a town might group itself, but they were never, in their beginnings, an integral element of normal municipal life. They existed for the empire and for themselves, and the fact that they protected munici palities was incidental.
After Rome, here and there, the citadel recovered its impor tance. The growth of feudalism meant the decline of the free, or nominally free, city. It should not be said, however, that in feudal times citadels ceased to be built ; sometimes the right of fortifica tion was granted by a lord and sometimes it was acquired by arms; the lord's castle might be a true citadel, or a new one might be erected by the city-State. As a type of architecture distinguished from the castle, the modern citadel is generally said to date from 1568, when the duke of Alva built one to dominate Antwerp. But the rapid multiplication of small States in the late middle ages made the citadel common in Europe.
See for architectural bibliography, CASTLE ; FORTIFICATION AND SIEGECRAFT ; Daremberg and Saglio, Dict. ant. class., "Acropole"; Planat, Enc. archit., "Citadelle"; C. Enlart, Man. archeol. fr.