In 1564, duca Emanuele Filiberto ordered the construction of a massive defensive citadel for his new capital, Turin. Francesco Paciotto, a military architect, was put in charge of the project which took thirteen years to complete.
The pentagonal, star-shaped citadel was constructed on top of the bastion Saint-Pierre, built during the French occupation of the city, at the southwest corner of the city. Typical of urban fortresses, two of the five bastions point toward the city, and a cleared area stands between the gatehouse and the developed area within the city walls. Construction of the fortress required levelling an entire neighborhood, including the Chiesa dei Santi Martiri; legend holds that artifacts such as monuments, columns, plaques and statues, and other treasures of antiquity were used as fill material within the redoubts of the citadel.
The fortress is surrounded by a moat, dry due to the rapid drainage of the soil. Within the citadel is a huge cistern with a winding ramp to provide the defenders with a protected water supply during an extended seige fed by the water from the Po River. Artillery is mounted on the bastions.