The Third Dynasty of Ur or Ur III was a Sumerian dynasty based in the city of Ur in the 22nd and 21st centuries BC (middle chronology). For a short period they were the preeminent power in Mesopotamia and their realm is sometimes referred to by historians as the Neo-Sumerian Empire.
The Third Dynasty of Ur is commonly abbreviated as "Ur III" by historians studying the period. It is numbered in reference to previous dynasties, such as the First Dynasty of Ur (26-25th century BC), but it seems the once supposed Second Dynasty of Ur was never recorded.