The Greek civilization was one of the most advanced of its time, and it had many important things to leave to the world. Most of the things that the Greeks managed to invent, write, discovered, were preserved in the Roman literature, or rather the Latin literature. There was lot of Greek literature in Alexandria, where the biggest library in the world was located, but it was burned down, and most of the literature in it was destroyed. The Roman legacy was largely preserved though, and within the Latin literature there was lot of the Greek legacy translated into the language of the Romans, which later found its way to the people that started off the Renaissance at the end of the Middle Ages.
