1. The city was invaded by Alexander the Great during 331 B.C, as a result, he overtook and took most of the people as slaves.
2. As the city was very old already during its time, people stopped giving importance and the civilisation s l o w l y started to fall apart. Just like the Romans. Even if they had a wealth of knowledge.
3. It became under Persian rule, The Greeks fir the last 3 centuries before it vanished.
4. The city therefore became derelict. All the statues and 'amazing' buildings which once were, all the building materials were stolen and cannibalised by working-class peasants.