Troy was an ancient city on Earth.
According to the Greek author Homer, the city was besieged and destroyed by the Greeks in a war in about 1200 BC. Upon seeing Yeoman Teresa Ross, Trelane remarked on her beauty inquiring if hers was "the face that launched a thousand ships and burnt the topless towers of Ilium?" (TOS: "The Squire of Gothos")
The city was rediscovered in the 1870s by the German archaeologist Heinrich Schliemann. According to Richard Galen, this discovery counts among the greatest archaeological discoveries of all time. (TNG: "The Chase")