The ships of the vikings, if we may judge from the few specimens preserved in the museums of Denmark and Norway, though well built of their kind, were not much better than large open boats, undecked, averaging about seventy feet long, and drawing not more than four feet of water. They had only one mast with a square sail, and they trusted rather to rowing than to sailing for their progress. Except on the largest ships, about fifteen or sixteen men at a time, with a like number relieving them, and sixty or seventy fighting men, or a hundred in all, may have been the complement of a viking ship. There was no difference between prow and stern, and the vessel could be worked in either direction, the steering being managed by an oar at the side. The high-pointed prow at either end was often fashioned into the likeness of some animal, generally a dragon or a serpent. It is evident that such a craft as these, however well adapted for navigation in the long sheltered fiords of Norway, would not be very safe in an Atlantic storm.[115] It is probable, therefore, that the Northmen would be careful observers of the weather, and would generally choose a season of calm weather for slipping across the German Ocean. Once arrived at the English or Irish coast, they would choose some island near to the mainland and make it their lair, from whence they might issue forth to plunder and destroy. Especially convenient for their purpose, as for that of their Saxon predecessors, were such islands as Sheppey and Thanet, separated from fertile Kent only by narrow channels in which the dragon-ships could lie sheltered from winds and waves. Dear also to the heart of the Northman buccaneer were the estuaries of great rivers, Humber, Severn, Thames, Seine and Loire. Here they could collect their ships, scattered perchance in the course of their passage over the ocean, could watch the movements of the militia gathering for the defence of the country, and then at the right moment could row rapidly up the broad stream, capture and sack some unsuspecting city, and gather great store of gold and jewels from some rich cathedral. This, the collection of treasures from the more civilised lands of the south, was, after all, the chief incentive to the early vikings in their wild sea-rovings. Herein they were like the first generation of Elizabethan adventurers in the Spanish main, to whom the plunder of the Plate-fleet seemed the supreme object of desire, though with the viking, as with the buccaneer, thoughts of settlement and of conquest came later, and they who had come to ravage remained to rule.