Assassin Den

Assassin Dens were towers used by the Assassins as headquarters, and a means of monitoring a city or district. They were ideal locations for the Templars as well, who staged many attacks to claim the dens for themselves.

Many dens were used across several Mediterranean cities during the 16th century, with eight found scattered in the districts of Constantinople.

Defense
The Ottoman Assassins fought to defend each of their dens in Constantinople, however, a Master Assassin, such as their leader Yusuf Tazim, was often needed to personally oversee and direct the defense. By Mentor Ezio Auditore da Firenze's arrival in the city in 1511, he aided them by acting as General for some of these attacks as well.

Should an Assassin apprentice complete his or her training, he or she could be assigned as a particular den's Master, and protect it without the help of any other higher-ranked Assassins.

Despite successfully repelling an attack, the Templars would often send further attempts to take the den, particularly should the Assassins become notorious within the city.

The Assassins of Constantinople closely aided many other nearby cities as well, and would establish dens within them to increase their influence on the local populace.

Reclamation
Should ever a den fall to a Templar attack, they would place their own guards around it, and work to defend it from a reclamation attempt.

Similarly to Assassin Master Assassins, Templar Den Captains would be assigned to guard a den. However, often on these occasions, Ezio would use his talent to identify the Captain and eliminate him.

Upon doing so, simply lighting the signal fire atop the tower of the Assassin den would signal the Templars that their Captain had fallen, and most would withdraw without a fight.

Constantinople dens

 * Galata headquarters
 * Galata Den
 * North Imperial Den
 * Southern Imperial Den
 * North Bayezid Den
 * South Beyazid Den
 * North Constantine Den
 * South Constantine Den
 * Piri Reis's Shop

Trivia

 * Templar Dens and their Captains are the conceptual evolution of the Borgia Towers of Rome, the twist being the Byzantines will reclaim the Den if the player's notoriety is too high.
 * Replacing a Templar Den with an Assassin Den will switch nearby Templar guards in the area with Ottoman guards, who will still react to crimes, but are not immediately hostile.
 * Retaking a den will increase the amount of ziplines in the district.
 * Each Den comes with a bomb-crafting station and a map to access Mediterranean Defense.
 * Once a Master Assassin is assigned to a Den, it becomes locked and can no longer be attacked.
 * In the Mediterranean Defense, you can have your apprentices build dens in other cities and occupy them. Five maximum per city, making so you can have up to 65 other Apprentices alongside your normal team.
 * On top of steeple in every Den there is an Assassin insignia.

Source

 * Assassin's Creed: Revelations