Destroy the Monument, or DTM is a gamemode in which a team must completely destroy the other team's monument(s) to win. Tradionally, monuments are 1x2 or 1x3 obsidian towers, but there are some unique exceptions in both size and block type. In these cases, it is possible to break a monument with TNT as well as a pickaxe.
In single monument maps, the monument is normally in the center of each teams side. In the case of there being several monuments, they are almost always set up equidistant from the other monument(s). Some maps include XML to change the block of the monument after a certain time frame, to make destroying the monument easier. Defending the monument is dependent on the geography of the map, but the most common defensive tactic is to clear as much land as possible around the monument, to bedrock if possible. This helps keep the monument in open view, so that defenders can see if someone is attempting to destroy the monument.