Answer:
a long narrow trench dug in the ground
Explanation:
According to these ines from the poem "For the Union Dead", the poet talks about Shawn's father not wanting any other monument except the ditch where his son was thrown.
The use of the word "ditch" as used in this context means a long narrow trench dug in the ground. This is because, it is described as a place where his son was thrown.
