From Suetonius’ LIVES OF EMINENT GRAMMARIANS

XXIV.  MARCUS VALERIUS PROBUS, of Berytus [903], after long aspiring to
the rank of centurion, being at last tired of waiting, devoted himself to
study.  He had met with some old authors at a bookseller's shop in the
provinces, where the memory of ancient times still lingers, and is not
quite forgotten, as it is at Rome.  Being anxious carefully to reperuse
these, and afterwards to make acquaintance with other works of the same
kind, he found himself an object of contempt, and was laughed (523) at
for his lectures, instead of their gaining him fame or profit.  Still,
however, he persisted in his purpose, and employed himself in correcting,
illustrating, and adding notes to many works which he had collected, his
labours being confined to the province of a grammarian, and nothing more.
He had, properly speaking, no scholars, but some few followers.  For he
never taught in such a way as to maintain the character of a master; but
was in the habit of admitting one or two, perhaps at most three or four,
disciples in the afternoon; and while he lay at ease and chatted freely
on ordinary topics, he occasionally read some book to them, but that did
not often happen.  He published a few slight treatises on some subtle
questions, besides which, he left a large collection of observations on
the language of the ancients.