Quintus Marcius carried out a heroic march into Macedon through the tough mountains of the Olympus range. He sent 4,000 light infantry ahead to secure the road to a pass near Octolophus, but the road was so difficult and steep that they advanced only fifteen miles and seven miles the next day. They spotted an enemy camp guarding the pass. Quintus Marcius stopped on a hill, which gave a wide view and ordered one day's rest. The next day he attacked with half of his troops. The enemy had seen the Roman camp and was ready. The narrow ridge allowed only for the deployment of small numbers of light troops and so the engagement was limited to a skirmish between light troops. Perseus, who was not far, did not intervene or send more troops. Despite the presence of the enemy, Quintus Marcius had no choice but to persist. Leaving some troops to guard the summit, he marched across through trackless places, having sent forward a party to open a road, with allied troops protecting them while clearing the way through the forests. Marcius kept the cavalry and baggage before him and closed the rear with the legions. The descent from the hill was tough; the pack animals often fell. In impassable steeps the elephants threw off their riders and roared loudly, frightening the horses. A series of bridges (made with two long posts fastened to the earth to which ten-yard-long beams were attached) was made where the rocks were steep, in order to help the elephants. The Romans advanced only seven miles, and then waited for the troops at the camp to join them. On the fourth day they reached a pass and encountered similarly difficult terrain. As they got close to the plain some troops encamped between Heracleum and Libethrus, while some occupied a valley and part of the plain. The greater part was on hillsides.