The ancient elves left no roads but left many ruins in far-flung locations (mentioned on multiple occasions to multiple people; this has always been Morrigan's test to see who'll put it together)
Eluvians are of interest to Corypheus (Morrigan's was taken en route to Skyhold in the Hinterlands by Venatori and Red Templars, there was Venatori interference in retrieving Merrill's from Kirkwall)
Known to some: that the eluvians are why the elves didn't need roads, and that they aren't - as is believed in some writings - merely for communication but rather travel. There are letters documenting this. Leliana has visited the Crossroads with Morrigan. (This series of letters can have been compromised)
Morrigan and Merrill agreed to keep the truth of the eluvians hidden at the time given the dangers posed by and to them. (This series of letters can have been compromised)
A small team ventured through Morrigan's eluvian to reach Merrill's in Kirkwall (being sworn to secrecy about them): Inessa, Ellana, and Thranduil all know
The Medicine Seller and Morrigan have spoken of the eluvians and their purpose; he put together the far-flung ruins with no roads to connec them to understand that eluvians are doors
to be updated in a more ic fashion later, if your character has more ic knowledge to be shared please make a new comment so I can come back and edit this thanks!
ic eluvian knowledge; please don't reply to this comment!
to be updated in a more ic fashion later, if your character has more ic knowledge to be shared please make a new comment so I can come back and edit this thanks!