Due to the nature of tabletop RPGs, a campaign will often start with a random group of strangers. Here are some ways to get them adventuring together, without resorting to the old Tavern trope.
In the Temple Square of The City, where the nine Greater Gods have their houses of worship, a sudden flash of light blinds (perhaps permanently) all those who are nearby. When the light has faded, a tiny, naked baby is lying in the doorway of each Temple. The Gods, it seems, have come into the world - but why?