In 1554 and again in 1556,[1] Ferdinand named Busbecq ambassador to the Ottoman Empire under the rule of Suleiman the Magnificent. His task for much of the time he was in Constantinople was the negotiation of a border treaty between his employer (the future Holy Roman Emperor) and the Sultan over the disputed territory of Transylvania. He had no success in this mission while Rüstem Pasha was the Sultan's vizier, but ultimately reached an accord with his successor Semiz Ali Pasha.