William of Rubruck
Friar William of Rubruck, who visited the court of the Great Khan in the 1250s, listed "the Blac", or Vlachs, among the peoples who paid tribute to the Mongols, but the Vlachs' territory is uncertain. Rubruck described "Blakia" as "Assan's territory" south of the Lower Danube, showing that he identified it with the northern regions of the Second Bulgarian Empire.