The skull that Peterkin finds is the dominant symbol of the poem. It is an actual physical relic from the battlefield. Other elements of the battle, such as the corpses rotting in the sun, are recalled by Kaspar but date from the distant past. The skull exists in the here and now. 

The children have not seen a human skull before. All Peterkin knows is that it is “a large, and smooth, and round” (Line 12) object. The innocuous description conveys nothing of the true nature of the skull. In this context it is a powerful symbol of the battle and the price the struggle exacted in terms of human lives. It is no surprise to Kaspar, however, who says he has seen many such skulls in the area. He takes the skull from the boy and likely remains holding it as he tells the children about the battle (See: Further Reading & Resources).

A ploughshare, a metal tool used in farming that cuts the top layer of soil loose, is mentioned once in the poem. Kaspar states that when he ploughs his land, the ploughshare turns up the skulls of men who were killed in the long-ago battle.