Any reason my Catapults won't attack buildings/structures?

I select the unit and move the cursor, which is the falshing 'Movement' cursor, to an object. Instead of changing to the 'Attack' icon it stays in the Movement display. If i click the Catapult unit moves towards the position i selected.

Any ideas?

Click on the building/structure you wish to attack...it should bring up an option in the right window that will allow you to "attack with cat#_".

Its not always possible to attack a building even if you see it. You need to have troops or an outpost in wieving range.
There are also some spots in the "greyed" range of the cats that arent valid targets. Its a bug I guess.

I see.. i was going about it all wrong.. thanks for the help.

Don't forget to protect the cats from melee enemy.

Also, don't use cats to take the retaliation away from a stack of heavy calvaries. And disbanding them might be a waste, too.