research for historical novel. Two questions

[Nathan Ross]

The epistolary approach was used to very good effect in John Williams' novel Augustus

Also Thornton Wilder's The Ides of March mile:

Letters would be a better idea than a diary, I'd say - a diary would probably record only things of mundane interest (Marcus Aurelius's Meditations, literally 'To HImself' is written as a sort of philosophical journal, but this sort of thing would be the rare preserve of the aristocracy).

Letters, on the other hand, were intended to communicate and so would be a better vehicle for interesting stuff. Also, quite a few Roman letter collections survive. Have a look at these, written by Claudius Terentianus, an Egyptian recruit to the Misenum fleet, to his father back at home:

Terentianus letters

I think Renatus might be right about the inscription too...