Manipur Cavalry is a technology in Age of Empires II HD: Rise of the Rajas that is unique to the Burmese and can be researched at the Castle once the Imperial Age is reached. Once researched, it gives Arambai and cavalry +6 attack against buildings.
Strategy
The Burmese lack the Siege Onager and the Siege Ram. Manipur Cavalry powers up the Burmese Battle Elephants' raiding capabilities so they can compensate for that.
It must be mentioned that Masonry and Architecture combined give buildings +6 armor, nullifying the effect of Manipur Cavalry completely. The only unit that can actually use the bonus attack against buildings with Architecture is the Battle Elephant since it has an attack bonus against buildings and with Manipur Cavalry it can keep it up even against buildings with Architecture.