Sevastopol, situated on Crimea’s Black Sea coast, was a closed city and home to the Black Sea fleet during Soviet times. Sometime friends who wanted to visit would arrange for Sevastopol residents to smuggle them into the city in the trunks of their cars. After Ukraine became independent, control of the Black Sea Fleet became one of the most contentious and potentially dangerous issues dividing Russia and Ukraine. The Ukrainian government formed a Ukrainian navy, resulting in a split of the fleet, with some officers and sailors pledging an oath to Ukraine. In 1997 the governments of Russia and Ukraine signed a partition treaty establishing two independent naval fleets with designated armaments and bases. Ukraine is leasing parts of its bases to the Russian Black Sea Fleet. The ruins of an ancient Greek colony at Khersones, which dates back to the sixth century BC, are situated on the outskirts of Sevastopol. Excavation of the ruins, which include a basilica, began in the early 1800s. Khersones is a UNESCO world heritage site.