We may well connect and condense the chief results of our study in this chapter. It seems to be clear that a culture essentially similar to that of the European lake dwellers existed at Anau, in the piedmont zone, a little north or northeast of the Iranian plateau, with which it had trade relations. The oldest turbary forms of domesticated animals appear here at least 1,500 years before the founding of the Swiss lake dwellings. They were mostly introduced from some mountain region, the nearest probable source being the Iranian plateau, but their first domestication may have taken place equally well elsewhere in western or central Asia, or even in Arabia. Susa shows similar remains extending back into a far more remote past; and the similarity or kinship of the pottery in the oldest strata at Susa and Anau and elsewhere leads us to believe that a culture similar in other respects also was widely distributed at this time. We can hardly doubt that agriculture was practised by the founders of all these settlements. We can only frame conjectures as to the origin of agriculture. It seems to have been introduced by the women of hunting and fishing tribes. The first agricultural implement was probably the digging-stick, which was followed by the hoe. Hoe-culture is still common in Asia and Africa. Finally, during the first part of the Bronze period, or perhaps somewhat earlier, the plough drawn by cattle and guided by a man superseded the hoe as a means of breaking up the soil for the culture of grain. CHAPTER VI MEGALITHS Megaliths, those great stone monuments of prehistoric time, have always excited the wonder and interest of all observers.[86] Under the name of dolmens or stone chambers, cromlechs or stone circles, tumuli or mounds, they form a striking contrast to the insignificant and ephemeral thatched huts of wood and clay which formed the homes of the living. These chambers, especially those of later date, are often accompanied by circles or radiating lines of rude pillars, the Menhirs or standing stones. In the more fertile and densely populated regions the great blocks have been removed and used in the foundations of buildings. They must once have been far more numerous. But Déchelette reports nearly 4,500 as still existing in France;[87] England contains almost or quite as many; and they are very numerous in Denmark and Sweden. We will mainly follow Sophus Müller in his study of these monuments in Denmark.[88] The simplest, and apparently the oldest, dolmens are the small rectangular chambers consisting of four stones set up on edge with one large one forming the roof. These are usually between 5 and 7 feet in length, 2 to 3-1/2 feet wide, and 3 to 5 feet in height. One of the end stones is shorter, leaving an opening under the roof through which one may reach or even crawl into the chamber. Somewhat larger chambers of the same type and having five or six wall stones are not uncommon.