Before you can attack Orcish Hordes, you must set up a good platform to support you army. You need to be able to support at least 30 Units. You need to research Weaponry, Armour, Spell of Healing, Elemental Summoning, Rain of Fire, and upgrade your arrow strength. Researching spell of Invisibility and Far Seeing. Training Faster and stronger horses for your knights will help, but you really don't need to.
 
Step Two : Building gates for your city.
To keep Orcish Hordes away from you city, you must build a good gate, where your men can enter, but Orcs cannot. You must build a good gate, because you main gate can be used for offense as well. (And we will use it as a trap)