The Embrace (Speculated)

Esteemed Waterdhavian historian Ciara Perthford spent several months visiting Daring Heights during one of its earlier summers, having heard about some encounters with ancient Yuan-Ti burial sites. Perthford was fascinated by Yuan-Ti history and spent her time interviewing adventurers who had been to the site before its destruction (in her words 'a devastating loss', in adventurers' words 'not a moment too soon'). She even visited the site several times, taking notes and sketches of what she could to examine further. Below is an excerpt from her scroll on the subject, detailing her hypothesis on the extent of ancient culture on these lands.

"...which confirms the estimated depth of the crypts proper at between 280-340ft, a depth on par only with sites found in Chult. The existence of a deep mausoleum in the Sunset Spine mountain range solely dedicated to the internment of Yuan-Ti dead, combined with the importance it clearly held for the people given the presence of a genuine superweapon and powerful guardians suggests two things. Firstly, that this was an area of great importance to merit the dedication of such protection. Secondly, that there must have been Yuan-Ti nearby to be dying in such quanitities, and this implies settlements, even a kingdom. I will explore this idea, calling it for simplicities sake The Embrace, as the mausoleum was called Mershhaulk's Embrace.
Given estimated internment at the mausoleum, there must have been a sizable population living in the Embrace. Reports suggest the western face of the Sunset Spine leads to a desert, which is the preference for some variants of reptilian humanoids, but no evidence thus far suggests that any Yuan-Ti have ever favoured this terrain, or mountains themselves. This leaves East as the most likely site of their civilization. The larger the settlements were the more evidence would have been left behind. Given the relative dearth of such evidence I hypothesize that the Embrace consisted of numerous small villages and gathering points, with buildings constructed mostly out of semi-permanent materials like hide or plants.
There are two further points of interest in the area to consider. A long forgotten temple to Tharizdun was discovered some time ago, in the hills south west of Daring Heights. This temple, though not a Yuan-Ti deity, suggests different groups have lived in this area over time, a topic for future study as more evidence emerges. The other point is the simple existence of the large swamplands to the east of Daring Heights, about 2 full days travel east of the mausoleum. Again considering the scale and importance of this burial site, clearly placed on high ground out of respect and reverence for either its occupants, its purpose in fueling a superweapon or other less overt reasons, it is reasonable to suggest that one might travel a few days with the (dis?)honoured dead to bury them in such an important place. Allowing for this journey would mean the existence of a Yuan-Ti civilization of multiple small settlements spread throughout a large swampland area, a little different to the more centralised structures we encounter with classic Yuan-Ti structures seen today in Faerun.
An archipelago-like society dotted throughout what is colloquially known as The Frog Bog would require a governmental structure of some bureaucracy. Taking into consideration the typical cultural aims of the Yuan-Ti of Faerun and the ruins found, I would posit this to have been a theocracy, with priests running each small community, not dissimilar to some hamlets found in more parochial parts of Cormyr or the Sword Coast. For the Yuan-Ti this would be perfectly in keeping with known facts and would allow the priests to be directing the flow of the deceased to the mausoleum for their addition to the rites and experiments they were performing there.
Given the topography and biodiversity found in the Frog Bog presently, one can imagine the diet of the Kantasian Yuan-Ti to consist......."