Bigger and Bigger

I watched a construction crane go up today at a building site across the street.   Erecting it took most of the day.  What was most interesting to me was the leveraging of the tools.  Each section of the crane tower arrived on a flatbed semi.  It's hard to tell the scale from a distance, but they must each be 40-50 feet tall.

First, a normal size mobile crane would unload the section from the trailer and stand it upright.  Then the task was passed off to a much larger mobile crane that rose perhaps 20 stories into the air.  This machine was able to lift the section over to the ever-growing crane tower.  Then the section was lowered into place and quickly fastened to the section below.

The two workers on the tower would then climb the ladders of the new section and await the next.