In addition to the Germanic powers that he associates with his ashplant, and possibly some ancient Celtic ones as well, Stephen thinks of it in Proteus as his "augur's rod of ash," associating it with Roman powers of divination.

JH 2017

A Roman augur holding a lituus, from the Swedish encyclopedia called the Nordisk Familjebok, first published in the 1870s. Source: Wikimedia Commons.