E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Salt Hill (Eton).
The mound at Eton where the Eton scholars used to collect money from the visitors on Montem day. The mound is still called Salt Hill, and the money given was called salt. The word salt is similar to the Latin salarium (salary), the pay given to Roman soldiers and civil officers. (See MONTEM, SALARY.)
Cakes of salt are still used for money in Abyssinia and Thibet.