The pass is easily defended. On both sides, towards Cleonae and towards the plain of Argos, may be seen traces of ancient works built to defend the defile. Near the highest point of the pass, where the road begins to descend towards Argos, there are low Turkish watch-towers called Derweni on both sides, and rough stone walls such as the Greeks threw up in many passes during the War of Independence. In 1822 the Turkish army under Dramali Pasha, retreating from the plain of Argos, was caught by the Greeks in the pass of the Tretus and nearly annihilated; for years afterwards the defile was strewed with skeletons and skulls of men and horses. “Every part of the Argolic plain,” says Leake, “is considered unhealthy in summer, and the heat is excessive; that of the ravine of the Tretus, in the mid-day hours, is said to be something beyond bearing, which I can easily conceive, having passed through it in August, at an hour in the morning when the heat was comparatively moderate. Not long since a Tartar, after having drunk plentifully of wine and raki at Corinth, was found to be dead when the suriji held his stirrup to dismount at the khan of Kharvati (Mycenae), just beyond the exit of the Tretus.” The name Tretus (‘perforated’) was supposed by the ancients to be derived from a great cave in the mountain where the Nemean lion had his lair. As to the ancient name of the pass, and the supposed wheel-marks in it, W. G. Clark says: “This is the road known by the name of Tretos, or ‘the perforated’; not, I conceive, in consequence of the caverns in the neighbouring rocks, which are not more numerous hereabouts than elsewhere, but because the glen is, as it were, _drilled_ through the rock. And drilled it has been by the stream which flows at the bottom. We saw, or fancied we saw, frequent wheel-marks in the rocks, and we know that this was the direction of a carriage road. But from my subsequent observations I learned to distrust these marks. The ordinary mode of carrying wood in Greece is to tie the heavier ends of the poles on each side to the back of the horse or donkey, and suffer the other ends to trail along the ground, thus making two parallel ruts which in course of time may attain the depth of and be mistaken for wheel-tracks. When a depression is once made, it becomes a channel for the winter rains, and so is smoothed and deepened.”