The Ritual stone.
The Ritual marker is a carved ancient stone located at the Mahjarrat Ritual Site (also known as The North) where the Mahjarrat meet around every 500 years to sacrifice one of their own and rejuvenate, reclaiming their lost powers and youth in the process, becoming much more powerful. It is an ancient artefact that plays an unknown role in the rituals of the Mahjarrat and is strongly bound to the spot, the only known way to move it is to destroy it and build again in another area, much like the Mahjarrat Bilrach did with the original marker. For centuries, the Ritual marker's location was unknown until Tale of the Muspah, but it was not seen until the Grandmaster quest, The Ritual of the Mahjarrat. In Tale of the Muspah, the Zarosian Mahjarrat Jhallan hibernates under the stone, in an icy cavern. According to Jhallan, he is 'directly under' the Ritual stone. However, it turns out that the stone was a few steps north of his location.
Before the player obtains the Frostenhorn during the Temple at Senntisten quest, the area is much more covered in snow, as proven in the flashback during the Nadir Fremennik Saga. This is due to the horns ability to magnify any energy around it. Due to it being in the cold weather for such a long period of time, it magnified the temperature, causing the deep freeze in the area.
The marker seen today is actually the second version of the Ritual Stone, created by Zaros in the Second Age[1], and eventually relocated to its current location at Ghorrock.[2] The original was left in Freneskae after the Mahjarrat left with Icthlarin, presumably because it was bound to the area like the current one is.
The Ritual Marker before the player removed the Frostenhorn from Ghorrock, much more covered in snow than it is today.
In Nadir, Moia, the daughter of Lucien, embarks in a mission to find the Mahjarrat Bilrach. Upon reaching the bottom of Daemonheim, Moia discovers Bilrach in a room with a broken version of the Ritual Marker, which he claims to be the original, brought to him in pieces by Hearthen. It is confirmed in the first episode of "Above the Lore" by Mod Osborne that this is, in fact, the original marker from Freneskae.