For each of the towers, gather these 4 walls.  Not the direction (up or down) on the slots on the side of each wall.

Slot together 2 of the walls with opposite slot directions

Add a third wall slotting in place as shown

Slot the final wall in place

Locate the 4 corner braces.

Glue the corner braces into the slots on each corner of the tower wall as shown above.

Locate the top

Glue the top on with the barricades sticking up through the slots in the top.

Gather 9 wall studs

Glue the wall studs into the slots in the barricades on top.