Make the four walls and roof. Measure and cut five pieces of cardboard at 12-inches by 10-inches. Draw or paint a brick pattern on four of the five pieces. Cut out a downward U shape curve on the front wall. Assemble the four sides with the brick pattern into an upright, three-dimensional square. Glue the corners of each side together. Glue the remaining cardboard piece to the top of the square as the castle roof.
Create the eight pillars. Cut four, 12-inch tall cardboard paper towel holders straight down the middle -- so you end up with eight, long halves. Draw or paint brick patterns and windows on the outer surface of each half. Cover and glue one half onto each Bastille corner. Glue each remaining half at the center of each of the four walls.
Cut and paint 1/2-inch cubes of hard or soft foam. Glue the cubes around the perimeter of the roof -- leaving 1/2-inch in between each cube -- to create the facade of the roof line.
Take the u-shaped piece of cardboard you cut out and lay it down flat in front of the wall opening. Glue the bottom corners of the drawbridge to the base of the Bastille. Cut and glue two strands of twine or faux chain to the top corners of the drawbridge and upper corners of the front wall opening. Cut in half and glue low-density polyethylene bottles -- plastic water bottles, for example -- to the outer base of the Bastille. Be sure the drawbridge is positioned over top the polyethylene. Fill the polyethylene with water to create the Bastille moat.