By early 1452, work began on the construction of a second fortress (Rumeli hisarı) on the European side of the Bosphorus, several miles north of Constantinople. The new fortress sat directly across the strait from the Anadolu Hisarı fortress, built by Mehmed's great-grandfather Bayezid I. This pair of fortresses ensured complete control of sea traffic on the Bosphorus  and defended against attack by the Genoese colonies on the Black Sea coast to the north. In fact, the new fortress was called Boğazkesen, which means "strait-blocker" or "throat-cutter". The wordplay emphasizes its strategic position: in Turkish boğaz means both "strait" and "throat".