Xianfar

Xianfar was a ziggurat used by the aliens, before the forces of the US Army destroyed it. This Ziggurat was one of the main targets of the attack and the only one hit by the humans, therefore it gave the name to the battle that took place there, which is known as Battle of Xianfar. Xianfar was later thought to be the generator that brought the aliens on earth, since the vast explosion suggested that it held a large amount of energy.

Actually, Xianfar didn't make the fleet of Ziggurats travel through space, it brought entire solar systems to the location of the ziggurats in order for the overlords to conquer them. After that, the systems were sent elsewhere again so that the next solar system could follow. With Xianfar destroyed, earth  was now the aliens' home too.