World Overview

Cumae: The Orbis is a D&D Campaign world and fiction setting first used in the summer of 1987 and grounded in the middle ages of Eastern Europe, Byzantium and Persia, as a break from the Western European tropes and the heavy influence of JRR Tolkein; not that there's anything wrong with that, but he did it well, and there's no need to reskin it yet again. Let's do something a little different.
The religious life of the world strives to model a more realistic Gnostic/Syncretic models of the Roman Empire in the late classical Mediterranean and the Golden Age of Byzantium. The people, even the 'evil' people, beseech all the Good gods/angels/spirits/forces - not just a single patron deity - for favor and protection. Evil or unfavorable deities are bribed with offerings, magically bound or propitiated to stave off trouble.
Most ritual is performed under the assumption that God(s) - good and bad - are capricious, jealous, and liable to offense; the Christian concept of a loving, self-sacrificial god is foreign and unknown. Morality is founded as much on the civilizing principles of Imperial Law and the need for a stable economy as on any edicts on behavior from one or another deity or pantheon. Moreover, different denominations exist within the faiths and the cults, and debate (and occasional violent disagreement) over theological quandaries is common. Different calendars are used by different cultures as an extension of their differing religions, with different events marking the 'Year 0' in different regions of the Orbis. Incidentally, this account is written from the perspective of the Archivists' Guild operating the Teniel Library in Khazigur, and uses the calendar and date-fixing conventions of the Khazigiri Empire, which date year 0 from the fall of the Cumaean Empire and the rise of the first Autarch a little more than 12,000 years ago.
The Orbis is old, and has a long memory. Writing was invented over 70,000 years in the past on the Orbis, and mountains of written histories exist in complete forms--not a mere 8,000 or so years of history as on Earth. The survival rate of libraries during regime change is much more positive on the Orbis than on the Earth as well, so quite a bit has been preserved, recopied and reprinted from the distant past. Moveable type has existed for over 8,000 years, but what the Orbis does lack is any reliable kinetic power source such as steam technology (though the Gnomes are close to it) or electrical power in non-magical, usable form, so printing presses are still hand-cranked, and most technology is still based around single innovators, animal or humanoid power, and where the expense is not too great, magical power.
The Orbis draws a lot of its terminology and some of its 'feel' from the fantasy works of Gene Wolfe, especially the Book of the New Sun, but this is not Earth of a million years in the future; it's some quantum variation on Gnostic Byzantium from another universe entirely. Michael Moorcock's Gloriana, Edgar Rice Burroughs and HP Lovecraft also flavor the world's locations, people, magic, and technologies.