D3: The Vault of the Drow is the last of the D-Series modules and sees the party arriving in the underground drow city Erelhei-Cinlu. It is the lengthiest in the series so far and with good reason: the module abandons the more linear dungeon crawl progression of the previous installments for a more open-ended approach.

This marks a dramatic point in D&D’s evolution from scenarios intended for tournament play (even though D3 was a tournament module) to materials with a more naturalistic, even gestalt, feel. This pivot point changes the idea of what a campaign could be.

Up to 1978, a campaign was a series of dungeon crawls linked by the participating characters. They amount to a kind of chute, perhaps with many intervening branches, which eventually lead to the same place: a now-empty dungeon and a group of wealthier, more experienced player characters. D3 eschews the chute for a number of hubs, or encounter areas, which exist in a sort of narrative web (pun sort of intended, sorry). Players choose which hub to visit and, presumably, their actions there can affect the state of the other areas when they arrive.

This takes some of the power of the DM and gives it to the players, allowing them to decide not just the overall arc of the story, but the order of the beats as it goes, leading to fewer dungeons intricately designed in a vacuum and more improvisational play.

Though Gygax’s Greyhawk and Arneson’s Blackmoor existed since ’72, I think D3 marks the first step toward the campaign settings we know and love today, where source books present vast swaths of information, not to present a definitive believable world, but rather to provide players and DMs the resources so they, together, can cobble together their own.

Final thought: that demon on the front cover kind of has a Creature of the Black Lagoon look to it (it’s the stripes that do it, maybe?) and it also sure seems like it was on the mind of whoever designed Molasar in Michael Mann’s film adaptation of The Keep.