The first self supporting vaults
Retainers' tombs from a royal mastaba at Sakkara. The dead had been put in a square pit roofed with wood and bricks covered by two vaults. The facade was finished with smooth plaster and the owner's name and profession was carved into wooden tablets (note that only the recesses remain today). Time: c. 2.700 BC in the reign of king KŠa.
Source of pictures: George Emery, Great Tmbs of the First Dynasty, book 3, plate 116.