Roman Emperor Marcus Aurelius wrote his famous "Meditations" during his campaigns against the barbarian invaders.
Probably one of the first, and definitely one of the most famous ancient books on personal improvement and attitude towards life, this will be enjoyed by many because of similarities with some modern blogs(although in an ancient language).
His private journals record the passing thoughts, maxims, and musings on life and death of a sensitive and humble mind trained in the Stoic philosophy which, to a certain extent, anticipated the development of Christianity.