The history of Six Spires Pass is mostly noted in the Histories of Gladnor – the full chronicle of the Kingdom of Gladnor.
Some of the history of this locale is built as part of A living world setting wherein Content is updated continuously. as part of the Campaign Records of the Steel Realms.
The Curtain of Night (in this area) was robbed of some of its power as part of the effects of The Odyssey of Elancil’s Wound. It retreated eastward for dozens of miles around CY 8400, taking a hundred years in some cases to regain the lost ground.