Thasian rebellion
The Thasian rebellion was an incident in 465 BC, in which Thasos rebelled against Athenian control, seeking to renounce its membership in the Delian League. The rebellion was prompted by a conflict between Athens and Thasos over control of silver deposits on the Thracian mainland, which Thasos had traditionally mined. The rebellion was eventually crushed in 463 BC after a long and difficult siege, but not before Sparta had secretly promised to invade Attica in support of the Thasians. The Spartans were prevented from making good on this promise only by an earthquake in Laconia in 464 BC, which triggered a helot rebellion. Thucydides cited the Thasian episode as one of the incidents during the Pentecontaetia which marked the transformation of the Delian League into an Athenian empire.