Originally Posted by Marquis of Roland
My thoughts on Pelennor:
There were four separate armies assaulting Minas Anor. One from Mordor, Sauron's own men, one from Minas Ithil, the Witch King's own army, one from Far Harad, and one of Easterlings from beyond the sea of Rhun. Plus another army of dark numenoreans from Umbar, better known as corsairs. All these armies totaled up to possibly 200k.
The city was defended by I believe only 4-6k men (it would've been cool if they shown the provincial troops coming into the city like in the book). Add this number to the 6-8k relief force of Rohirrim cav, plus a couple more thousand provincial troops Aragorn brought in the ships.
When the Rohirrim charged, the 6k cav would have probably broken about 20-30k men, but going at the speed they were going, plus going into densely packed infantry formations, it wouldn't have mattered if the infantry ran or not: they would have eventually bogged down hitting all those dead bodies, or tripped over dead bodies, something. The orcs needn't be brave, they just needed to be THERE.
As soon as they broke one army however, there were 3 other armies arrayed against them on other parts of the field. Those could have easily came up and folded the Rohirrim flank while they were charging. 6k men on horses is nowhere NEAR enough men to break 200k.