These were written during WWI or II for the most part, Mere Christianity were originally radio addresses given by lewis during bombing raids and other wartime calamity (or so I think.) and as such are probably not yet in the public domain. I've read Screwtape Letters, it's a wonderful little bit of theology and a great mental exercise, I've got to pick up a copy of Mere Christianity.
"Works and Days" is great it's like a manual for the life of the Greek farmer, The Theogony is great too, I'd suggest that too, it's {as the title suggests) the Greek creation myth where you see Zeus rise to power and stop the momentum of the other gods so he remains King of the Gods.
