Not sure if this helps, but this is personally what I did:
Pre-battle:
- Upgrade all units to maximum level.
- Upgrade Varangians as much as you can.
- Have a ton of war drums at the ready.
- If you have POH, then get Khalid and Nur Din along with their weapons. If not, skip this step.
Battle:
- (IAP) Place Khalid and Nur Din on their respective units.
- Place Justinian and Theodora immediately. Their technology is extremely important for getting all your units across the river.
- Throughout the entire battle, try to utilize all of your resources to it's full potential.
- The charge cavalry in the back is already sufficient; send it to battle immediately. For Pasha, use his forced march ability and equip him with a regular transport ship. Use him to block the enemy.
- Orhan is pretty much useless. Because of this, his mobility doesn't matter much so just put him on a regular transport ship.
- Rest of the units go through the castle for additional/replacement units.
- Don't bother trying to take the first key city. There's a very low chance that you'll actually get it. If it is open, do take it and have a strong general camp it.
- Wipe out the enemy attacking the city and send a general to block the northern and southern reinforcement passages.
- IMPORTANT: Quickly take out the Byzantine general. This dude somehow destroys everything in his path and if he camps the last key city it's game over.
- Cautiously rush to last key city, using a siege war gear to get it down faster. Make sure your strongest generals are at the front so they can actually open the city.
- If you're lucky, you'll have successfully taken the last key city and you're on your way to the next level.
I know this a lot but then again this is one of the harder levels. Good luck!
