[Eric in the Ozarks]

You can lay siege to walled cities if time is not an element, surprise is wasted and you don't mind turning in a lot of casualties.

[SoCal Pubbie]

In Europe of the Middle Ages, laying siege was THE way of conducting warfare. Pitched battles on open fields was too risky- you might lose your whole army in a single day!

Conducting a siege usually meant just surrounding a city and starving it out. Unless a relief force was on the way, there was no need to do much more than fling a few dead horses and diseased corpses over the wall with the trebuchet your engineers just built.