Fair churches still attest Visby's devotion, great walls its military strength. Undefended towns, famed for their wealth, were almost as unsafe in the early middle ages as they would be to-day. Visby unwalled suffered much. In the _Saga of Olaf Tryggvison_ we read how one of the Earls of Ladir (p. 69), driven forth by that king, "took such rede that he gat him a-shipboard and went a-warring to gather wealth for him and his men. First he made for Gothland, and lay off there long in the summer season, waylaying ships of chapmen who sailed toward the land, or of the vikings else; and whiles he went aland and harried there wide about the borders of the sea." But at least our fathers had the advantage over us that in the intervals of all this fighting they did not need to be practising the oldest of the arts. They knew not our crushing burdens. The same hands held the account-book and the sword; the same ships plowed the sea for trading and for war. Thus from the turbulence of neighbours the most peaceful of cities has left us some of the most impressive examples of military architecture that all Europe has to show. During the thirteenth century the burghers walled their town. The defences are of solid stone and make a bean-shaped circuit of two miles and a half. For 1,950 yards they run along the shore, where to-day is the Students' Walk between the lofty walls and a line of tall trees. The original height of the walls was fifteen to eighteen feet, according to the ground. Wide battlements, each second one pierced by a small embrasure, frowned along the top and just behind them was the customary parapet-path, sustained by a series of arches within--a very common way of economising materials from Roman to latest times. Much stronger were the walls from having two moats towards the land without, and on the north side there were three. Three older structures--little towers--were built into the walls, and so remain to-day. The Krut Torn, or Powder Tower, clearly named in later days, looks over the sea; the Tjärhof, or tar-house, and the Mynt Hus, look over the land. The tar-house is clearly known from a use to which it was degradingly put in latter days. There was a mint at Visby in the thirteenth century, and there seems to be no evidence whatever that it was not in this Mynt Hus. Six towers were also built to strengthen the wall, all toward the south; one of them is round, established on a jutting rock. One is known as Kejsar Hus, or Cæsar's Tower, named evidently because connected in some way with the Holy Empire of Rome.[76] For Roman indeed was the Empire still when these proud walls rose. As we have already seen, the sovereign was for ever straining his eyes towards the ancient city of the Cæsars, there to receive the Imperial Crown, in Italy to exercise imperial sway. A little later in the century, Horace Porter[77] thinks about the middle, more towers were added and, on the east, barbicans to enfilade the moats.