These string bundles were called _quipus_, but though quipus are still to be found in collections, the art of reading them is altogether lost. The Chinese histories, Mr. L. Y. Chen informs us, state that a similar method of record by knots was used in China before the invention of writing there. The Peruvians also got to making maps and the use of counting-frames. “But with all this there was no means of handing on knowledge and experience from one generation to another, nor was anything done to fix and summarize these intellectual possessions, which are the basis of literature and science.”[120] When the Spaniards came to America, the Mexicans knew nothing of the Peruvians nor the Peruvians of the Mexicans. Intercourse there was none. Whatever links had ever existed were lost and forgotten. The Mexicans had never heard of the potato, which was a principal article of Peruvian diet. In 5000 B.C. the Sumerians and Egyptians probably knew as little of one another. America was 6000 years behind the Old World. XVII SEA PEOPLES AND TRADING PEOPLES § 1. _The Earliest Ships and Sailors._ § 2. _The Ægean Cities before History._ § 3. _The First Voyages of Exploration._ § 4. _Early Traders._ § 5. _Early Travellers._ § 1 The first boats were made very early indeed in the Neolithic stage of culture by riverside and lakeside peoples. They were no more than trees and floating wood, used to assist the imperfect natural swimming powers of men. Then came the hollowing out of the trees, and then, with the development of tools and a primitive carpentry, the building of boats. Men in Egypt and Mesopotamia also developed a primitive type of basket-work boat, caulked with bitumen. Such was the “ark of bulrushes” in which Moses was hidden by his mother. A kindred sort of vessel grew up by the use of skins and hides expanded upon a wicker framework. To this day cow-hide wicker boats (coracles) are used upon the west coast of Ireland, where there is plenty of cattle and a poverty of big trees. They are also still used on the Euphrates, and on the Towy in South Wales. Inflated skins may have preceded the coracle, and are still used on the Euphrates and upper Ganges. In the valleys of the great rivers, boats must early have become an important means of communication; and it seems natural to suppose that it was from the mouths of the great rivers that man, already in a reasonably seaworthy vessel, first ventured out upon what must have seemed to him then the trackless and homeless sea.