Why was the city of Alexandria built?

Egypt in the time of history had several capitals from the first capital Memphis at 3100 BCE until Sais at 332 BCE. Alexandria was selected by Alexander the Geat for its location and he personaly marked all the places of interest, the state house, the palace, the market, the library, the agora, the theater and the city perimeter where the city walls would be built at 332 BCE before his second encounter with the Persian army and Darius at Issus [331 BCE].

The purpose was to supersede Naucratis as Hellenistic center of Egypt and to link the valley of Nile with Greece.

The city remained the capital of Egypt until the first rule of the Muslims at 641 AD/ CE.