As the description says, beat this level on Hard.
This level introduces you to a larger beast. The trick is to shoot it in the back, preferably with Church's grenade launcher. The other thing that may be helpful is that the gladiator always goes after you when you attack it, so you can station your squads (using the commands) to a point behind the beast, and lure it away so that it faces away from them. Your team can do some damage that way. It also allows you to get Church around behind it while you're luring it away, and then switch to her to unload with your grenade launcher.
After the gladiator, you'll find yourself across a chasm from some centurions that keep being replaced. Jones has to possess the one on the right and pull the lever to cut them off. Once you've killed all of them, Church will need to do a button sequence to reach the other side.
Perhaps the most confusing part of the level is that there are three tiles on the floor, two on one side and one on the other, that you need to extend a bridge. The problem is that when you take Church to the other side, you can't go back to move the team to the tiles. The tiles on the other side are in the middle of the small columns; use your squad commands (left and right on the d-pad) to order them to the tiles while you stand on the one in the middle of your side. Then the bridge will extend, allowing you to continue.
While the game isn't particularly difficult on Hard, there are some cheat codes that can help you if you get stuck.
1. Go to the Bonus Codes screen.
2. Go to the game's pre-order site: http://www.codemasters.com/jerichopreorder/index.php?shop=ga...
3. Copy/paste this as a pre-order code: AGEH-56JW-X2GB-DN1N-EGUT
4. On your Bonus Codes screen, you'll see a number. Enter it.
5. Enjoy your infinite ammo and faster health regen. The health regen definitely helps in the levels where you have to not die for the achievement.
There's a separate code for "Dominator Damage" that you can get by registering your game at www.codemasters.com/register. That further increases the damage that your weapons do.
Due credit to http://www.cheatcc.com/xbox360/clivebarkersjerichocheatscode...