Ambam

Ambam is a large fortress city built into the largest mountain pass in the range of mountains that border the northern side of the Shindusian valley. It was originally founded following the conquest of the Kuchu valley to its north by Shindus as a way to secure the land holdings they had conquered and prevent a subsequent invasion into Shindus proper, should they be unable to hold the land. 
Its development was spearheaded by the 10th representative of Dorelion, who saw an opportunity to create a city unlike any other. He ordered his builders to dig into the complex cave systems high up in the mountains and use the stone they cut from it to create the fortress. The final product was a massive fortress that covered the entire entrance to the mountain pass and hung nearly 100 feet above the ground. The cave system also makes the fortress much larger than it appears from the outside, providing nearly four times more usable area than the fortress itself. And after it was completed and had military reserves placed in the fortress, a city began to build up around it as people came from the south to settle the new land. It started off as people building houses down into the valley below, but some people even took up residence in the cave systems. Only a few decades after the fortress was finished, it had already become the second largest city in Shindus, behind Lukrar.
However, after the Fall from Grace a century later and the disappearance of the representatives of Pitelion, the people who previously inhabited the Kuchu valley rose up in resistance. With their crushed morale and a significant loss of military might, Shindus was unable to keep their hold on the lands beyond the mountain pass. Eventually, the only presence that Shindus had in the Kuchu valley was Ambam, and if it fell there was a good chance the rebelling forces would be able to push into Shindus proper.
This conflict lead to a year long standstill between the two forces. The Kuchun forces were not able to properly siege the city, as it was still perfectly capable of being resupplied, but they also couldn't make any definitive attacks because its defenses were so strong. And any time Pitelion's Army attempted to push out past Ambam, they were quickly forced back in as they could not sustain a fight in the valley. In that year, basically everything in the city not located on or inside of the mountains was razed to the ground and Ambam went from being the second largest city in the nation to not even being considered a city.
Eventually, an uneasy peace was brokered between Shindus and the reestablished Kuchun Dynasty, and Ambam was able to rebuild somewhat, although it still hasn't reached anywhere near what it was at its peak.