Press Pause and take a look at the map. The Knights on the left side of the map will at some point rush towards your melee units. Station your Heavy Camels near the pin of the rivers just below the Knights. They will shoot at them and damage them, so your melee units can finish the job.

Then, get your camels to the island next to the Sappers and move them up. Kill the Crossbowman and move them towards the pin of the river so they can pick off the pikeman that are patroulling in front of the walls. Next, move your camels alongside the edge of the map, up until they are in one line with the right diagonal corner of the defense turret. Some camels will start shooting, slowly picking off the archers and crossbowmen on the turret. It is important to watch your camels and the units on the tower! There is a sweet spot where your camels shoot, but they won't shoot back. After picking the tower clean, I recommend you save!

Use some of the slaves and move them towards your camels. Start moving from the top section of the wall down towards the gatehouse. They will uncover murder holes and also set off some of the pitch ditches planted here. After the fire is out, move your camels close to the tower, alongside the walls and clear the gatehouse. Once that it done, you can start killing the crossbowmen on the keep while stciking close to the walls and the tower.

Use some more slaves and send them alongside the walls towards the corner defense turret, uncovering pitch and murder holes again.

Clear the corner tower, then move up closer and clear the second gatehouse. Use sappers to destroy the top defense turret and send in the camel lancers with the remaining sappers to kill as many foot soldiers as you can. Once the gatehouse is clean, send in your heavy infantry and kill the Lord.