In just three lines, the poem sets a grand gesture against a quiet act of violence. The first line pictures someone touching the head of a king, which sounds almost tender or reverent, the way you might touch a statue for luck or respect. Then the poem turns. "For this" points to the price, and the answer is that a stone was wounded.
The word "wounded" is the key. It treats the stone as something alive, something that can be hurt. To make a monument, the stone has to be cut, chipped, and shaped, and the poem asks us to notice that damage rather than the glory of the finished image. The title, "Monument," sharpens the point: what we honor in public is built on something that was broken.
The speaker doesn't shout about this. The tone is spare and a little sad, with a hint of irony toward power. The mood is hushed and thoughtful, leaving us to wonder whether a king's likeness is worth what it took to make it.