Northeast of the town of Tulcea, you will find the ruins of the Aegyssus Fortress. The construct, whose name is of Celtic origin, was built by Greek colonists in the 4th century B.C. atop Monument Hill (Dealul Monumentului). Later, the fortress was conquered by the Roman army, shortly before the birth of Jesus Christ, but retained its status as a military fortress overlooking the Danube. In the 11th century the fortress was destroyed before it was taken over by the Ottomans during their occupation of Dobruja.