This is a medieval wagon designed to help in scaling walls of fortified castles and such.  It's rather big so it's being pulled by two large creatures, but a team of horses could replace them or a company of soldiers with a few design tweaks.  It has a compartment that can fit a group of men so they don't have to worry about getting shot by an arrow on the way to the wall at least.  The carrier creatures are heavily armored with slabs of iron so they are well protected, and when the wagon is parked next to the wall they are either released or simply aren't of any concern as now the defending soldiers have men climbing the ladders to contend with.  Furthermore the wagon can drive along the wall to drop men off at lesser guarded spots.