Ever wonder how they actually built those giant tower cranes you see at construction sites around the world? Well, the actual construction process may surprise you, as it doesn’t involve any helicopters or aerial vehicles to help haul in the pieces. Continue reading for the video.

Simply put, self-erecting cranes are a type of tower crane that lift themselves from the ground or lift an upper, telescoping section using jacks, allowing the next section of the tower to be inserted at ground level or lifted into place by the partially erected crane itself. They can thus be assembled without outside help, and can grow together with the building or structure they are erecting.