Call it what you want, whether it's Break the Monument, Destroy the Pillar, or whatever you so choose, but here it is.
This is the arena. The void is void that players can edit, and any blocks that are stone are also a void barrier that cannot be built on. (I don't have worldedit, so I couldn't actually make them void without more effort than it's worth.) Each team starts on a different side, and must bridge the gap by building. In the final arena, the void can be as large or small as you please, but preferably something that's at least 16 blocks, to make bridging a task of strategy.
The red wool is the entry point for one team, while blue is the entry point for the other. The chests each contain gear.
This is the chest that is next to the entry point. Obviously, for the real event, there would be several of these chests at the entry point, each filled with rows as shown that contain basic gear (I neglected to include bows and arrows, which could easily be placed in a separate chest. These are important for shooting opponents off of their bridges).
This is the other chest, which doesn't necessarily have to be where it is. The final arena ought to be much larger, with terrain and scattered chests such as these that contain other building supplies. Some could possibly even contain Power I bows or Feather Falling boots. Up to whoever makes it.
The obsidian/emerald pillars are the "monuments" that each team is trying to destroy/defend. To win, your team has to break all the blocks in each of them.
There you go. Do with the concept whatever you would like, but I think that it would be a fun event (although potentially a long one, depending on the size of the arena), and certainly not one for 1v1 battles. Preferably a 2v2 minimum team would work. Also, some way for the teams to re-enter their entry point after dying would need to be implemented. Feedback is welcome.