Perseus panicked. He evacuated the area and all the strong posts, leaving them open to the Romans, even though the area was easily defensible. He ordered the inhabitants of Dium, where he was encamped, to move to Pydna and also moved his statues there. Quintus Marcius advanced, but he faced a difficult decision. The Romans could leave the area only through two passes: through the Vale of Tempe to Thessaly or on to Macedon by way of Dium, and both were guarded. The Romans could not withdraw to Thessaly lest they cut off their supply lines. Furthermore, the Vale of Tempe was a difficult passage, very dangerous even if it was not guarded. The precipices on both sides were very steep and there was a passage which was so narrow that there was barely room for a loaded horse. To make things worse, there were guard detachments in four places along the pass. One was at the entrance, another in a thick forest and the third on the road where the valley was narrowest (Livy did not specify the characteristics of the fourth). The only way to retreat or receive supplies was to cross the same mountains the Romans had come through, but they were also very difficult to pass. It was also hard to pass through unnoticed as the enemy was posted on the heights. The only option was the area between the bottom of Mount Olympus and the sea, but that was only a mile wide, half of which was the bog of the mouth of the River Baphirus and a large part of the remaining plain was taken up by the town. The small remaining space could be easily closed off by a short rampart with towers and the material for its construction was abundant.