The Athanatoi were a body of young men of noble status that was originally raised by John I Tzimiskes (r. 969-976) in 970 for his war with the Rus', where they played a decisive role in the battles before Preslav and during the Siege of Dorostolon.
[1] This reconstruction was part of an effort to address a major military crisis for the Empire, following the disastrous defeat suffered by the Byzantines against the Seljuk Turks at the Battle of Manzikert in 1071.
As part of the reorganisation process, the remnants of the provincial troops of the Eastern themata (military provinces) were brought together as the Immortals, providing a new element of the tagma.
[1] A schematic diagram of the standard field camp layout of the Byzantine army in the late 10th century shows the Immortals as deployed by the Imperial tent, within an outer square of Thematic units.
[6] The new unit fought under the future emperor Alexios I Komnenos in the Battle of Kalavrye (1078) against the rebel general Nikephoros Bryennios the Elder,[7] and are mentioned in the wars against the Pechenegs in the 1090s, but disappear thereafter, along with another contemporary creation, the Archontopouloi.