The City of Dead... This was what a person would have called the homeland of Titans if they had seen what happened here.
The only living beings in the entire city were the Titans inside the Royal Palace. Everywhere else, the Titans had already been killed and replaced by the Undead.
Normally, Karyk couldn't turn so many Undeads at once as the amount of mana needed was astronomical. Even at his peak, he had a much smaller undead army, which took him years to create.
However, this time he didn't have to worry about it. The mana needed to turn someone into an undead was taken from their own bodies after devouring them.
In essence, the Titans were paying for their own deaths, and that payment was used by Karyk to bring them back as Undead.
The more of these Titans he devoured, the stronger he and the abyss was becoming.