the right bank an enormous wall of stones, as large as a waggon could carry, so that if the river ran as usual with a moderate volume the city would not be deprived of the convenience of its water; but if it should be swollen into a flood a moderate stream would run as usual throughout the city, but the excess of water would be forced into this channel constructed by Justinian, and thus extraordinarily conquered by human art and skill might run round the back of the race-course, which is situated not far off. Moreover he forced the river within the city to run in a straight course, by building a wall above it on either side, so that it could not turn out of a straight path; by which means he both preserved the use of it for the city, and removed all fear of it for the future. The wall and outwork of Edessa, like those of the other places, had for the most part fallen into ruins through age; wherefore the Emperor restored them both, making them new and much stronger than they were before. Part of the wall of Edessa is occupied by a fort, outside of which rises a hill very close to the city and overhanging it; this hill was in ancient times occupied by the inhabitants, and included in their walls by an outwork, that it might not form a weak point to the city. Their work, however, made the city much more open to assault in that quarter; for their outwork was very low, built on an exposed site, and could be taken even by children playing at sieges. Justinian therefore took it down and built another wall on the top of the hill, which is in no danger of an assault from higher ground in any quarter, and which follows the slope of the hill down to the level ground on both sides, and joins the city wall.[44] [Illustration: EDESSA. _From Texier & Pullan’s Byzantine Architecture_ COLUMNS ON A TERRACE OF THE CASTLE.] Also at the cities of Carrhæ[45] and Callinicum[46] he destroyed the walls and outworks, which were much impaired by age, and rendered them impregnable by building the present complete fortifications; he also built a strong wall round the unprotected and neglected fort at Batnæ,[47] and gave it the fine appearance which it now presents.