I checked (and double checked) all the scrolls on this topic, but I am not trully sure to get my answer.
Who built exactly the ziggurat in the "monument of the ancient" ? The Imaskari ? An ancien human civilisation unknow, the same who built the Raven Forteress ?
I always thought the Sundering (-17000) killed also the first human civilisation who built the Citadel of the Raven (-18000)
Well you are asking questions to which no answers yet exist. Given its location the monument of the ancients could easily have been built by netheril (I don't recall if there is a date of its construction).
As for the citadel of the raven, it is a long way from the coast and so the elven sundering is unlikely to have affected it (it's purpose was to create evermeet I believe). Most likely the downfall of that civilisation was down to the death or destruction of its more advanced patron (dragon or giant, I forget which) that elevated the primitive humans to civilisation so they could be its servants.
I linked the monument of the ancients to a netherese arcanist named yrix alquinnar who specialised in summoning and binding outsiders (specifically elementals).
I have Citadel of the Raven as giant fortress taken over by orcs and then by Moonsea powers, lately by Zhentarim.
For pyramids and ziggurats I haven't decided yet between Mulhorandi and Imaskari origin. They should be one of those more likely Mulhorandi but then it makes little sense that they are found so far from their home. I haven't found any indication that Imaskari build structures like this. Does anybody know of any? Are there any pyramids in Calimshan area?
"Goodness is not a natural state, but must be fought for to be attained and maintained. Lead by example. Let your deeds speak your intentions. Goodness radiated from the heart."
The Paladin's Virtues, excerpt from the "Quentin's Monograph" (by Ed Greenwood)
Why an origin from so far away at all. Narfell and raumathar picked up magical expertise and knowledge from when they acted as mercenaries in the orcgate war. The artificers of horreb were possibly a nar tribe driven out by the unification of narfell who embraced the imaskari knowledge they uncovered or perhaps the mulhorandi empire they visited.
But that doesn't mean wherever you see a pyramid you have imaskari or mulhorandi influence. The pyramids at ascore and karse are without such cultural influences. It is likely that a pointed structure like a spire or pyramid is the best way to focus magic
Why an origin from so far away at all. Narfell and raumathar picked up magical expertise and knowledge from when they acted as mercenaries in the orcgate war. The artificers of horreb were possibly a nar tribe driven out by the unification of narfell who embraced the imaskari knowledge they uncovered or perhaps the mulhorandi empire they visited.
But that doesn't mean wherever you see a pyramid you have imaskari or mulhorandi influence. The pyramids at ascore and karse are without such cultural influences. It is likely that a pointed structure like a spire or pyramid is the best way to focus magic
I am inclined to say that pyramids are either shrines or magic focuses for elemental energies. That would lead me to Mulhorandi origin (which include Untheric people).
The "Monument of the Ancients" adventure from Dungeon 170 says that it was built "during the First Flowering by a lost civilisation of man" which would fit with the unknown human civilisation that built the Citadel of the Raven c-18000 DR. The same adventure also hints that at least some of the barbarians of the Ride are descended from that early culture.