Mavin's earthfast

Mavin's earthfast was a 10th-level Arcanist spell used in the days of Netheril.

History
The spell was created by Mavin around 3349 NY (−510 DR) However, after the near-cataclysmic destruction of the Weave caused by the casting of Karsus's avatar in 3520 NY (−339 DR) and the subsequent restrictions placed on magic by Mystra, the spell could no longer be cast.

Uses
It was originally created to allow continued mining of areas that would otherwise be too dangerous to mine. A casting of Mavin's earthfast made large areas of underground tunnels impervious to cave-ins and similar disasters. Its use was later adapted to preserve important areas of cities.

Spell components
The components needed for this spell were a stone of controlling earth elementals, six chardalyns (each imbued with transmute mud to rock), and an earth elemental.