In the 5th century BCE Sparta and Athens were the two major powers in Greece and it was perhaps inevitable that their spheres of influence would overlap and cause conflict. Sparta seems to have been particularly alarmed at the growing power of Athens, able to build an ever-bigger fleet of ships thanks to tributes from its allies and dependants. Sparta was also suspicious of the Athenians' project to rebuild their Long Wall fortifications which protected their harbour of Piraeus. In addition, Sparta was also concerned that inaction would push the other major Greek power,Corinth, to side with Athens.