Mount Lingon is the eastern and loftiest extremity of a great chain of hills; dividing Macedonia proper from Thessaly on the east and Epirus on the west. It forms a huge, triangular bastion, its northern base overlooking Macedonia, and its apex facing due southward, which is in fact the water-shed between the three great rivers, Aöus or Vioza flowing north-westward into the Adriatic, Penëus or Salamosia flowing eastward into the gulf of Saloniki, and Arecthus or Arta, which has a southerly course into the gulf of the same name, famous in after days for the naval catastrophe of Actium.[15] The flanks of this ridge are steep, difficult and heavily timbered, but its summits are green with rich, open downs, and watered by perennial springs and fountains, an admirable post of observation, and commanding the descent into all the great plains of Northern Greece. After mature deliberation, Philip retreated still south-eastward to Tricca, now Trikkala, on the Penëus; and, though with a sore heart, devastated his own country, wasting the fields and burning the cities. Such of the population as were capable of following his marches, with their cattle and movables, he swept along with him; all else was given up as plunder to his soldiers, so that no region could suffer aught more cruel from an invader than did Thessaly at the hands of its legitimate defender. Pheræ shut her gates against him, and since he could not spare the time to besiege it, for the Ætolians were coming up with him rapidly, having laid waste all the country around the Sperchias and Macra and made themselves masters of many strong towns, he made the best of his way back to the frontiers of Macedonia.