I made this cool little level by using the Single-Player custom levels system. This particular scenario is something I whipped up as a fun little "Rally Your Armies and Fight the Baddy" type deal.
Basically, you play as a facade of what Western Rome used to be. You fight and clash usurper generals, ending their dynasties as they themselves die (through commanders). This is a very historically accurate and fun setting in context, considering how often an entire civilization, army or kingdom can collapse with the mere death of a central figure like the King or General.
After you fight the Usurpers, you will find yourself dealing with the Barbarians. Either eradicate them on the sight, going on a manhunt for their commander, or put up minimum defenses and prepare for the greatest threat of them all : Attila the Hun. You see, Attila starts out as the beefiest of all in this Level. He will tear through Eastern Rome, Parthia and the Visigoths. You do not have time on your side at all. The kill ratios have been changed to 3/9 for attack and 4/9 for defense, forcing you to cobble massive armies for rather small defending armies.
But by the time Attila has eaten through the East, you should have a force that can stand on 2 legs just fine. You should at least.
Something I rather enjoyed about Custom Levels ; being able to customize the names of AI slots. Very useful and nifty for creating environments and giving context to settings! I would love to see this feature extrapolated to Multi-Player, allowing Players to assume a role. You could then click on the Scenario's name for a slot to see the player pulling their strings, etc.
anyway, here's some achievements for the game, a short list.
Western Rome Unified - Survive until all Usurper Generals have been eliminated (all the slots named after people except Attila the Hun)
Ends of the Earth - Control Persepolis and Caledonia Superior
Solid Foundation - Control Magna Italia bonus by Turn 12
Scourge of God - Play as Attila and win by Turn 30
Champion of God - Defeat Attila by Turn 40
Hispania Rush - Control Hispania by Turn 17
The Path of the Usurper - Play as any Usurper General and win.