Students sometimes get fascinated by the idea of litter from the past: things left behind for other people to clear up—or not. One sixth former had visited Orkney and was interested in the wrecks left behind in Scapa Flow when the Germans scuttled their Grand Fleet in June 1919. Not all the ships were salvaged, and some are still there. Later, on a visit to Spain, he had seen a pile of murex shells left on the beach by Phoenicians, which was the waste from a purple factory: and he had connected the two things. Did we know, he asked, of other such blots on the landscape left behind from the classical era—things not put there to last, but simply left behind?
One obvious example is the siege ramp piled up by the Romans, or rather by their prisoners of war, against the rock of Masada in AD73, in one of the final campaigns of the Great Jewish Revolt, led by Lucius Flavius Silva. The ramp, which took several months to build, is still there, as a reminder of how thorough Romans could be when determined to put down a rebellion.
Not really a blot on the landscape, or not by now anyway, are the siege works left behind by Julius Caesar after he captured the fortress of Alesia (now Alise Sainte-Reine, in Burgundy). It was the final campaign against Vercingetorix, who was there in person and surrendered to Caesar in the best royal manner, arriving on his horse and ritually stripping himself of his armour.
There, with the warm fertile soil, the gentle process of nature has covered up the mounds and ditches and huge circumvallations —a double wall at least eleven miles in circumference and again a monument to Roman determination when faced with revolt. This greening and softening of the landscape is in contrast to Masada, out in the dry desert and stark in the burning sun.
An account of that remarkable episode in the Gallic War, after which the whole of Transalpine Gaul became a Roman province, can be found in De Bello Gallico, Book Seven.