"What never fails to astonish at Skara Brae is the sophistication. These were the dwellings of Neolithic people, but the houses had locking doors, a system of drainage and even, it seems, elemental plumbing with slots in the walls to sluice away wastes. The interiors were capacious. The walls, still standing, were up to ten feet high, so they afforded plenty of headroom, and the floors were paved. Each house has built-in stone dressers, storage alcoves, boxed enclosures presumed to be beds, water tanks, and damp courses that would have kept the interiors snug and dry. The houses are all of one size and built to the same plan, suggesting a kind of genial commune rather than a conventional tribal hierarchy. Covered passageways ran between the houses and led to a paved open area--dubbed "the marketplace" by early archaeologists--where tasks could be done in a social setting."