The 'congress' met again in the spring of 480 BC. A Thessalian delegation suggested that the allies could muster in the narrow Vale of Tempe, on the borders of Thessaly, and thereby block Xerxes's advance. A force of 10,000 hoplites was dispatched under the command of the Spartan polemarch Euenetus and Themistocles to the Vale of Tempe, which they believed the Persian army would have to pass through. However, once there, Alexander I of Macedon warned them that the vale could be bypassed by several other passes, and that the army of Xerxes was overwhelmingly large, and the Greeks retreated. Shortly afterwards, they received the news that Xerxes had crossed the Hellespont.