Similar to Pratchett in terms of humour - an author by the name of Jasper Fforde.

Pertaining to Rome - the Masters of Rome series by Colleen McCullough (nice and thick - several of them, an inch and a half each - glorious). Also, Ross Leckie has some on the Punic wars.

I'd put in a shameless plug for my father's book here, but that'd contravene my code of attempting to maintain anonymity.