Castel Sant'Angelo
The Castel Sant'Angelo was a significant, cylindrical fortress located on the northwestern edge of Rome during the Renaissance period. An end point to the Passetto di Borgo, Ezio Auditore da Firenze scaled the Castel Sant'Angelo in 1499 during his infiltration of the Sistine Chapel. It contains the highest point of any Assassin's Creed game. It is also the residence of Rodrigo Borgia, as he spends most of the time in the Castel.
Liberation of Rome
The Castel is the most heavily guarded building in Rome. In 1501, it was guarded by Lucrezia Borgia when Ezio infiltrated it, both to rescue Caterina Sforza, and to assassinate Cesare and Rodrigo Borgia. However, though he successfully rescued Caterina, he was unable to kill either Templar leader, after he discovered that Rodrigo had not been in the Castel for some time, and that Cesare had left moments after Ezio had arrived.
Later, in 1503, Ezio once again infiltrated the Castel. At a window along the wall of the fortress, he witnessed the murder of Rodrigo Borgia at the hands of Cesare. Ezio also found out the location of the Apple of Eden, thanks to Lucrezia, after realizing what kind of man her brother was. [1]
Rift
One of Subject 16's coordinates is located here. Jump across the beams in the water (the same way you go in the mission to rescue Caterina). Once you reach the first group of guards, climb up the ladder and then up the wall to your right (again the same route from the mission). Head left on the walkway towards the hay. Jump to the tower directly across from you, there should be a round window. Use eagle vision and the rift should be just below you. Drop down, catch it, and enter.
Achievement
The achievement/trophy "Fly Like An Eagle" can be earned when Ezio jumps off the pinnacle height of the Castel (the top of the flagpole) with a parachute.
Trivia
- If the player looks closely at some of the doors, they'll find Alexender carved into the stone.
- Throughout Sequence 5, the large door near the four papal guards and the fence accessing the lower courtyard are closed, so completion of the "Fly Like An Eagle" achievement is not possible until further game progression. The completition of this achievement can be achieved by climbing to the very top of the gient flag pole on top of the castle, which is believed to also be the highest point in the map of Rome.