Stone Age people in Britain were building large stone monuments as early as 4500 B.C., which makes them among the earliest massive builders in the ancient world. Archaeologists think that construction on Stonehenge itself began around 3100 B.C., with the enclosure of a large circle with an earthen bank. The actual construction of the monolithic structures began between 2000 and 1500 B.C., and involved moving the stones from a location 20 miles north. The stones contain evidence of smoothing with hammers, as well as tongue in groove joints, beveled edges, and the use of perspective. Unfortunately, there is no strong evidence as to how the builders moved the stones, but it is probable that they used rolling logs underneath to move them into place, and that they built earthen mounds as scaffolding to put the lintels, or the massive capstones that sit atop some of the monoliths, in place. The rest, it seems certain, was simply manpower, and it is equally certain that to marshal the sort of workforce needed to build the monuments, that the ancient Britons must have had a very organized, highly stratified society.