How should you go about a siege without quality infantry?

[GFX707]

Learn the heavy cavalry "blitzkrieg".

Buy 2 Onagers and break a hole in the wall, then pile all your heavy cavalry through the hole while sending your infantry (or light cavalry) close behind....the cavalry destroys whatever is guarding the breach, and then you speed your heavy cavalry to the square and the infantry (or light cavalry) tangles up any forces coming back down from the walls....kill everything in the square with your cavalry, wait 3 minutes....you win.

Perfected this technique with the Armenians and Scythians. You don't need any infantry to perform well in sieges....probably the best "doctrine" for sieging in RTW