There are two good places to level up your Crystarium when you come into the Archelyte Steppe in the beginning of Ch. 11. The first one can be found in the Southwest Corner of the main map, the Western Benchland. South of the pond, there is a peninsula where little birdlike characters mass around. At first this seems like an intimidating battle, considering that the enemies will summon characters making the battles very long. However, this can be remedied, if you have 3 of the following four characters: Lightning, Fang, Snow, and Sazh. You'll only really need the following paradigms: Commando x3 / Commando x2+Ravager / Commando x2+Medic / Sentinel+Commando+Medic / Sentinel+Medicx2. Set the base mode on Commando x3 and go into battle.

If you're able to get behind them it makes the battles all that much easier. Once you get the hang of things, you'll learn their pattern and be able to get them more often than not in a surprise attack. Have your leader, whomever you choose to have it attack with Ruinaga, followed by blitz. The Ruinaga will toss them into the air a tiny bit and hit multiple targets in a wide radius. The blitz should hit the same amount of people. Your support characters should attack with Blitz, Blitz, and then standard attack. The Ruinaga spell is important because it keeps the baddies from being able to mass a constant attack on you as well as keeping them unable to summon whoever they are going to bring into the battle. CP ranges from 2000 to 3500 for your 35-45 seconds of effort. If you're having a hard time, try Commando x2 + Ravager, and you may be able to juggle them a little, but the commandos really shred HP in this fight.

The second method should be undertaken when you've gotten more HP and strength, since the fights will be harder. North of the first point, there is a place where the big wolf and a behemoth are fighting. Hit them. Concentrate first on the Behemoth and take him out. Don't kill the wolf, since he's your buffer from being behemoth's lunch. Take them out, 6000+CP. Then turn around, jump down to the west and take out the 3 groups of wolfs for 2000-3000 CP. Repeat this and you'll have tons of CP in no time.