Lair of Romulus
The Lairs of Romulus are secret locations that are featured in Assassin's Creed: Brotherhood that act very similiarly to the Assassin's Tombs from Assassin's Creed II. Like the latter, there are six lairs in total, and completing each one will bring Ezio closer to gaining the strongest armor of the game.
As an equivalent to the Armor of Altaïr from the second game, Ezio will instead obtain the Followers of Romulus' greatest prize, their secret armor. While going through each of the lairs, Ezio will also learn more about this mysterious cult.
On the map of Rome, the locations of the Lairs of Romulus are marked by a Wolf Symbol and the actual Romulus treasure is marked on the map with an Orange Wolf Symbol.
Lairs and Locations
Palazzo Laterano - Inside one of the gardens.
Cloaca Maxima - Terme di Diocleziano (Note: Ezio must completely repair the Aqueduct that leads into the terme to access this, as the entrance is situated high up in the wall of the initially empty terme. However, the entrance can also be accessed without repairing the Aqueduct by dropping over the ledge and climb-leaping into the archway.)
Catacombe di Roma - Near the Piramide Cestia.
Terme di Traiano (Note: This lair is not optional, as Ezio needs to go through the lair in a Core Memory.)
Colosseo - Ground level between the inner and outer walls.
Basilica di San Pietro - Outside, near the staircase that leads to the inner garden.