Cavities within the cairn. Now cleared, the doorway opens into the dromos, or entrance chamber. Over 11 feet long and about 3.5 feet wide, the dromos leads to the burial chamber itself. The burial chamber walls, built of six courses of basalt boulders, slope slightly inward and support a roof of two massive slabs of basalt, one of which weighs more than 5.5 tons. The workman, right, leans against the burial chamber’s protruding roof. Behind him, a row of sandbags around the edge of the excavated area stabilizes the rocks.