Throughout the release of Space Marine and Adeptus Titanicus, numerous rules were published in white dwarf for new vehicles, infantry and titans for humans, Orks and Eldar. These rules, along with some new expansion rules, were released in a supplement for both games called Codex Titanicus.
For me, Codex Titanicus is up there as one of the best pieces of work put out by GW along with the two realm of chaos books, Rogue Trader and others. It is rich in background, art, imagery and rules. The book itself is atmospheric and carries across the era of the Horus Heresy.
It is divided into four main sections – section 1 includes new general titan rules and a campaign system and rules for new Imperial titans, vehicles and equipment. Section 2 has details on Eldar titans and infantry. Section 3 details the Orks and section 4 are the counters and datasheets.
There is also mention of "Codex Titanicus II" in the Space Marine rulebook. I have no information on what it was supposed to contain. I can only speculate that it'd include rules and articles that appeared in White Dwarf along with rules for Psi-Titans, Emperor Titans, Juggernauts and Zepplins. If anyone has any further information on Codex Titanicus II, I'd really like to know more. Please contact me at webmaster @ my domain name.
Update. Since posting above, I've discovered some rumour and hearsay about what else was to be included in Codex Titanicus 2: