The fifth-floor city Carl flooded, destroying the Dreadnought army and ending their participation in faction wars.
Larracos is the city Carl is famous for bombing. Other crawlers say he unleashed a feral god on the armies there, and Ian repeats the rumor back to him. Carl corrects it: he did not unleash a god — that is what they thought he was going to do — instead he helped flood the city of Larracos, and had intended to throw a god at them a few days later before they took his toy away.
The consequences dominate his hearing with Orren. The Dreadnoughts lost their entire army there and abandoned their stake in faction wars, and Borant, which had expected a different sort of attack, was left upset but probably richer.
A flooded city.
The site of Carl's fifth-floor masterstroke and the reason for his summons.
Also appears in books you've already read — spoiler-safe to their endings: