Gargoyles: Dark Ages
Gargoyles: Dark Ages, often abbreviated to The Dark Ages or simply Dark Ages, was one of seven proposed spin-offs, a prequel to Gargoyles taking place in Wyvern, Scotland in the years between 971 and 994.
The show was initially pitched to CBS, but not picked up.  It was first mentioned on Ask Greg as early as 1998, and beginning in 1999 the art pitch was regularly presented at the Gathering of the Gargoyles as a treat for convention attendees. 
At the 2008 Gathering, Greg Weisman revealed that he has a Dark Ages story in mind for the next six part Gargoyles miniseries. This story would be told after the conclusion of the Gargoyles: Bad Guys: Redemption story-arc, assuming the miniseries comics continue at that point.  In 2009, a possible name for the miniseries was revealed to be Dark Ages: Dream, and its story would cover "a substantial span of time". 
On April 19th, 2023, a soliticiation from Dynamite Entertainment appeared on Amazon revealing the release of a comic book. On Voices from the Eyrie, Weisman clarified that the first arc in the series, Alliance, is not the same story he had in mind as a follow-up to Bad Guys. 
Dark Ages would have been set at Castle Wyvern, beginning when it was built in 971, upon Kenneth II becoming King of Scotland.  It would deal with the beginnings of the alliance between the Wyvern Clan (then under Hudson's leadership) and Prince Malcolm, with Hudson and Prince Malcolm in the lead roles, Goliath, Demona (at that point named "Angel", short for "Angel of the Night"), and the Coldtrio in supporting roles, and the Archmage (who is allied with Iago) as a villain (although presumably one whose true nature has not yet been revealed to the Prince).  Hudson's mate would also be significant (considering her death also occurs in 971).  The trio are only children at this point, and would most likely have had a minor, possibly comic-relief, role.  Culen and the Illuminati would also have roles, likely as antagonists. 
With the gargoyles in 10th century Scotland largely nameless, Greg Weisman planned to use names to designate characters for the writers, artists, animators, etc (such as he did with Othello, Desdemona, and Iago on Gargoyles and Second, Sacrifice, and True (along with many others) in the SLG comic). If that wasn't feasible, Greg planned on having Prince Malcolm name every gargoyle with a biblical or mythological name, so that the humans on the show (and the audience watching it) could use those names while the gargoyles continued to ignore them. 
The series would have, if it had been made and continued long enough, covered the story of the Wyvern Clan between the foundation of Castle Wyvern in 971 to its fall in 994, including an account of how Princess Elena and Prince Malcolm died. (Greg Weisman has mentioned having strong ideas for how those events took place, but has not revealed them as yet.)  The Wyvern Clan's splintering into a second clan would have also been covered. 
By late 1997, Greg wrote "Once Upon A Time There Were Three Brothers...," a piece of prose fiction which serves as a sort of lead-in to the series.
In 2006, Weisman wrote another Dark Ages-themed piece of prose fiction entitled, "Hyppolyta". Weisman would eventually incorporate both pieces into Dark Ages "if and when the time came."