A Durance was a type of Forerunner memory storage device. Upon the death of a Forerunner, the individual's last memories and mental patterns were stored inside a Durance. The Durance and a bit of plasma from the immolation of the body were then presented to the closest family members of the deceased. Durances had a half-life of a million years. Their resting places were closely guarded by the family, such that the violation of a Durance was considered sacrilege. The Durance of The Librarian appears in Halo 4 and speaks to John-117 about the Ur-Didact and his plans.
- The Durances resemble, in function, the Prothean beacons from the Mass Effect game series.
- Coincidentally, the Protheans were also an Elder Race whose "supposed" technology was the basis for most of the technology used by the modern species of the galaxy.