Thinking they had the key to an easy victory, the Chaos commander split his forces and sent a pincer action against (what he thought was) the two weakest points on the city defenses.
Above & Below: At the Western gatehouse, Bretonnian knights and men-at-arms deploy outside the city walls. Most of the spell casters and supporting High Elf archers manned the battlements to fire over the defenders. (The defending commanders called it a "Helm's Deep strategy."
Below: The approaches to the gatehouse are well prepared, with the bridge over the creek demolished, rough ground and the small woodlands razed to prevent the Chaos attackers from having any cover and to slow their progress.
Above: In anticipation of such difficulties, the Chaos commander brought forward several Beast Herds and a unit of Furies, but they proved in effective against the hard metal of the Bretonnian Knights and were constantly pummelled by missiles and magic from the castle walls as they closed on the gatehouse. Below: To sum up the day, a lone Bloodbeast of Khorne avoids the "Business End" of a large unit of Grail Knights as they complete the mop-up outside the castle walls.
Below: While half of the forces were fighting at the Western Gatehouse, the other half were mustering at the Northwest Corner of the city to deal with the second Chaos pincer.
Below: To minimize damage from the defenders, the Chaos commander consolidated his units at the end of a pathway that was protected by a hill on the left and bordered by a large fetid swamp on their right. The view below is taken from a bolt thrower position located next to the service gate. The Chaos commander understood he would be unable to breach the citadel here, so he was looking to inflict as much damage as possible to soften up the defenders for the coming Skaven onslaught.
Above: Early in the battle, the Bretonnian Pegasus Knights charge the Chaos Lord on his dragon as they were flying across the marsh. The unexpected support of Khorne Champion on horseback (nearby) would be enough to drive away the Bretonnian unit.
Below: Several knights came through the service gate and lined up on the opposite end of the path against the seemingly small band of Chaos attackers.
Below: Incoming!! A well-placed Comet of Cassandora strikes the Bestigors behind the Chaos front line. While the Bretonnian knights handled their two units, the marauders (seen behind the comet) would succumb to a Master of Stone spell cast with Irresistible Force on the hill. Varduck the Heinous on his Chaos Dragon would cause some havoc inside the city wall, but the rest of his force would be routed from the battlefield on his return.