This is roughly how medieval engineers could have assembled a large trebuchet with the technology of their day, based on my experience and research. You can read more in the Journal of Medieval Military History, Volume XX.

The throwing arm here weighs around 370 lbs, and the counterweight box around 470 lbs. The shear legs themselves (the A-frame crane) likely weigh around as much as the box.

This was the first time I have used the winch for the halyard tackle on the arm, so we ran into some problems with redirecting the fall into the winch properly.

We might have been able to pull this off with just two people but I'm not sure.

You can see more of the assembly process in previous videos, starting a few years ago and going back forward to the present day:

Assembly Timelapse
   • Assembling the Medieval Trebuchet!  T...  

3-People Assemble this Trebuchet from Scratch
   • 3 People Assemble a 30-foot Medieval ...  

Lowering the Arm with Homemade Wooden Blocks
   • Lowering the 25-foot Tree on my Trebu...  

Emergency Disassembly
   • Medieval Trebuchet:  Emergency Disass...