From the Enemy's Eyes-Rohirrim Charge on Helm's Deep/Pellenor

[WarBringer]

Not only that, but remember that (especially in the movie version) the riders have not only the height given by riding on horseback, but also the higher ground they are charging from, increasing the speed of the horse and therefore the power of the charge. Think About it- even a stabbed horse, unless run throgh from end to end, will most likely go wwith gravity and fall foward, trampling the first line in much the same way that Theoden was eventually killed, so while pikes may be the most effective avaliable defense in Helms Deep, they still may not work. What does anyone think about siege weapons in this situation? the Uruks still had them...