Calith

Traditionally, Calith was developed and perfected during the reign of the Ancient Empire its unknown if it was developed with a purpose in mind or if it was a natural development in search of better building materials.
Unlike modern buildings that are made mainly of carved stone, Calith was poured into forms as a paste before it hardened into a seamless mass that appeared harder than granite.
Of the buildings from the time of the Ancient Empire, it's mainly the those constructed using Calith that are left standing, all others having been reduced to rubble from either the destruction that happened to the Ancient Empire, or the ever-marching forward of time.
The recipe for making Calith has been lost for millennia, but modern masons know it required limestone, ash, river sand, and water; yet every attempt to recreate Calith has produced inferior products. They are still impressive and are actively used in construction, but the precise same product has yet to be recreated. The masons believe that there are some ingrident that are missing from the recipe but have yet to find out what it is, other masons believe that they have hte materials they need, the problem is that while the materials are the same, they are at the same time not the same, in the sense that these masons believe that the ash they need must come from a specific volcano.
There are several myths around Calith, like that it only hardens when mixed at night under a full moon, or that elves were singing songs while mixing it, which made the material stronger than normal. The only theory that have some hold behind it, is that Sea Spirits might have been called to bless the mixture, this one is mostly dismissed because it have been tested, on several attemps, masons have called on spirits to bless the mixture and while it did make it stronger, it still didnt recreate the correct mixture.