The most impressive and famous of Sumerian buildings are the ziggurats, large layered platforms which supported temples. Sumerian cylinder seals also depict houses built from reeds not unlike those built by the Marsh Arabs of Southern Iraq until as recently as 400 CE. The Sumerians also developed the arch, which enabled them to develop a strong type of dome. They built this by constructing and linking several arches. Sumerian temples and palaces made use of more advanced materials and techniques,[citation needed] such as buttresses, recesses, half columns, and clay nails.