The king and his principal nobles had at times a few galleys or sailing-vessels of their own--almost, if not entirely, their personal property--and these they made use of for purposes of transportation or fighting when required; but during this period the maritime defence of the realm was carried out--on the whole inefficiently--on the hire system. The money for this purpose was forthcoming, since William revived a tax for defence purposes, called the "Heregeld", which had been not long before abolished by Edward the Confessor, on the pretext that by it "the people were manifoldly distressed". Had he not listened to the "little navyites" of his day, perhaps the Norman Invasion would not have succeeded. In addition to this, William placed the five principal ports commanding the narrowest part of the Channel on a special footing, under which, in return for certain privileges, they were to supply him or his successors with a fleet of fifty-two ships in cases of emergency. They could only be retained for fifteen days, however. These ports--Hastings, Romney, Hythe, Dover, and Sandwich--were then, and for ever afterwards known as the "Cinque Ports", though Dover is the only one which can still be regarded as a port at all. Rye, Winchelsea, and Pevensey also became "Cinque Ports" later on. William's idea with regard to the Cinque Ports was probably not so much the general defence of the kingdom as the defence of his communications with Normandy. With their assistance he could be sure of always being able to move troops either way across Channel as his exigencies required. Thus, when in 1083 William, who was then in Normandy, heard rumours of the intention of the Kings of Denmark and Norway and the Count of Flanders to invade England with a great fleet, he hurried over-Channel with so great an army that "men wondered how this land could feed all that force". Without the assistance of the Cinque Ports he might have had some difficulty in doing this. Although we really know a great deal about the ships of the Saxon and Danish periods of our history, we know comparatively little about those which were built between the Conquest and the accession of Henry VII. For, while we have had specimens of the actual Viking ships to work upon, we have for this long period, of over 400 years, little information beyond that afforded by the seals of maritime towns, the ships depicted by monkish chroniclers and romancists in their illuminated manuscripts, and in a few cases old stained-glass windows and decorative carvings. Now, to begin with, it is obvious that in each of these cases the artist was cramped for space. He had to decide between the calls of accuracy and of decorative effect, and almost invariably he gave way to the latter.