Tall alien structures built in the ruins of occupied cities.
They appear to function as command centres and landing bays for Alien airships and are heavily defended on the ground by contigents of mechs and skitters.
The top of the towers contain two landing bays at right angles to each other forming the shape of a cross.
Captain Weaver (an engineer in his post army civilian life) identified four main supports on the ground that could be destroyed causing the tower to fall .This formed the basis of the plan of attack of the various Second Massachusetts units upon these supports.
The attack failed due to advanced warning the aliens recieved from former harnessed child Rick.
Tower locations include Boston and Chicago and Los Angeles