Sandomierz (sändôˈmyĕsh) [key], Rus. Sandomir, town, Świętokrzyskie prov., SE Poland, on the Vistula. Founded probably before Poland accepted Christianity, Sandomierz became the capital of a duchy in 1139. It was razed by the Tatars in 1241 and again in 1259, but was rebuilt (14th cent.) by Casimir III and became (16th cent.) a flourishing trade and cultural center and one of the most beautiful Polish towns. A synod (known as the Consensus Sandomiriensis) held there in 1570 united all Polish Protestants. The town was heavily damaged by the Swedes in 1656 and lost its importance. It passed to Austria in 1772, to Russia in 1815, and reverted to Poland in 1919. Its most notable buildings are a 13th-century town hall and a 14th-century castle.