rebuilding of walls, the substitution of effective for inadequate mural defences, and the strategical modification of sites, went on continually throughout the Empire. Constantina, the new post of the Duke of Mesopotamia, was raised to the rank of a first-class fortress,[1] but the most elaborate works for the purpose of martial defence were executed at Dara, which still existed as the main bulwark against Persian invasion. The fortifications of Anastasius had been hastily built, and consisted of an uncoursed stone wall, laid without mortar, about fifty feet high. The town was exposed to attack over one stretch of ground only, as in its greatest extent it lay along the edge of a rocky declivity unassailable by an enemy. Justinian consolidated the original wall, closed its battlements so that they became mere loopholes, and raised it thirty feet higher. The towers were similarly treated and elevated until they overtopped the wall to an equal extent. A covered gallery ran through its whole length, from which the soldiers could assail the enemy with their arrows from the numerous loopholes. For still greater security, however, a second wall of smaller dimensions than the first, also with towers, but solid, was erected at a short distance in front of the first, and from the top of this rampart the main body of the military were active in repelling an assault. Lastly, a moat was excavated and led along so as to make a crescentic sweep from one end of the assailable wall to the other.[2] In addition to fortifying cities the Emperor built very numerous forts along the frontiers, and more than six hundred of these are named as being in the vicinity of the Danube.[3] Where the configuration of a region*
