For centuries Troy was thought to be a myth created by Homer or whoever composed the Iliad. No one knew where it was, so there was no archeological evidence to prove it was real. Then, in 1868, the wealthy German businessman Heinrich Schliemann discovered the remains of the lost city.
There is not a single Troy, but rather several piled on top of each other. In all we have,
Troy I -- 3000-2600 B.C.
Troy II --2600-2250 B.C. - richest of the first five
Troy III -2250-2100 B.C.
Troy IV --2100-1950 B.C
Troy V ---1900-1700 B.C.
Troy VI --1600- 1400 B.C. - the most advanced fortress (destroyed by earthquake). Only one arrowhead found.
Troy VIIa 1300-1190 B.C. - shrunken recovery of VI in 1300 B.C. destroyed by man in 1200. Mycenaean pottery found here.
Troy VIIb 1190-1100 B.C. - short-lived
There is no evidence of Troy before the beginning of the Bronze Age, and most likely began at the end of the line of Mesopotamian influence. The early city is referenced in Hittite texts implying at least a trade relationship between those two cultures. The successive Troys formed a stready march through time -- as devastating as each destruction may have been, a new one rose soon after.
As you can see from the diagram above, the fortress of Troy was actually quite small; unlike the massive city depicted in the movie Troy.
Troy VIIa is the stage chosen by scholars as the player in the Trojan War. There is a problem with the opponent, however. During this period Mycenae itself was under attack from the north so it seems unlikely that it could muster an attack on Troy of the magnitude described in the Iliad. Who then attacked Troy?