Rifts
Rifts appear to be breaks in the programming of memories within the Animus, which can be seen using Eagle Vision. Each of the ten are found on key landmarks throughout Rome, and conceal Subject 16's Cluster puzzles in Assassin's Creed: Brotherhood. They are the equivalent of Glyphs from Assassin's Creed II, but instead of revealing a second Truth video, they simply relay the message "The miracle is in the execution" along with an executable file. Accessing the file allows Desmond to go through a virtual obstacle course similar to an Animus Virtual Training Program mission, and ultimately receive a message from Subject 16.
Various hidden messages such as coded numbers and letters, music notes and morse code appear through the rifts.
Locations
Castra Praetoria
In the area where Octavien de Valois was assassinated, on the eastern wall.
Rosa in Fiore
On the north wall of the brothel, on the second floor wall.
Santa Maria dei Miracoli and Santa Maria di Montesant
On the western tower near the left dome.
Aventino
On the Borgia tower.
Castel Sant'Angelo
On the actual cylinder of the castle, on the south side where the top of the outer wall is closest to the cylinder, near a haystack, right below a circular window.
Caserma di Alviano
East side of the wall, on the outside of the perimeter.
Acquedotto Claudia
Near the small town where Leonardo frequently is located at, on the north side of aqueduct. Climb the Borgia tower to reach the top of the aqueduct.
Colosseo
At the very top, northern side of the Colosseo, just west of the View Point.
Palazzo Senatorio
On the back of the Palazzo, near the roof, towards the end of the free-running path.
Pantheon
Inside the Pantheon, on the wall right above the main entrance.