Playing as Byz, its 1171 and soon for the first time I shall be facing the mongol hordes ...

I've never played a faction in the east when the mongols arrive, and I must say I'm looking forward to it

Right now my strategy is to build big Castles in my steppe provinces and lightly garrison them. Then let the mongols expand when they arrive, leaving my little garrisons safe in sound inside their fortresses - if the mongols want to throw men away assaulting castles without siege artillery, more fool them.
Then, once they've run over a few provinces and spread their armies, counterattack in force - stacks of upgraded veteran Kats, Porno Cav & steppe heavy cav led by my high command generals

Was wondering what strategies people use to defeat the horde.