In June, the fleets transported the Allied expeditionary forces to Varna, in support of the Ottoman operations on the Danube; in September they again transported the armies, this time to the Crimea. The Russian fleet during this time declined to engage the allies, preferring to maintain a "fleet in being"; this strategy failed when Sevastopol, the main port and where most of the Black Sea fleet was based, came under siege. The Russians were reduced to scuttling their warships as blockships, after stripping them of their guns and men to reinforce batteries on shore. During the siege, the Russians lost four 110- or 120-gun, three-decker ships of the line, twelve 84-gun two-deckers and four 60-gun frigates in the Black Sea, plus a large number of smaller vessels. During the rest of the campaign the allied fleets remained in control of the Black Sea, ensuring the various fronts were kept supplied.
Try to answer this question if possible (otherwise reply "unanswerable"): Where was the port where most of the Black Sea fleet was located?
Sevastopol