- "The whole damn place is filling up with water. Help us, you bastards."
- — Last message from Tollen
Tollen was a city on Sera. Along with the city of Montevado, Tollen was destroyed by the Riftworm, under the direction of the Locust Horde, in the months before Operation Hollow Storm. It took only 18 seconds for the city to sink and flood.
The city was located near Tollen Dam and Speyer, and was approximately two hours away from Jacinto when traveling by King Raven. Long ago, when Tyrus was governed by nobility, Tollen was ruled by a duke for whom the Duke of Tollen's Regiment is named. The modern city was known for its dull, tall, and grim buildings and elevated highways, and was surrounded by suburbs and forest.
Following Emergence Day, Tollen managed to survive the initial Locust onslaught to some degree and remained under COG control. Dominic Santiago visited the city on several occasions during this period. It was eventually overrun by Locust and abandoned by the COG. Stranded then occupied pockets of the ruins. By 14 A.E., the COG had not ventured anywhere near Tollen in several years, and the only charts it still had of the area were six years old.
In the days after the Lightmass Offensive, the COG's geological survey manager received reports from refugees and Stranded that Tollen was flooding. Delta Squad, along with Sgt. Mataki, were dispatched via King Raven helicopter to recon the area. Upon their arrival, Delta Squad realized that water had not flooded the city; instead, the city had sunk and turned into a massive crater ten kilometers across, with only the edges of the city still standing. The lake was perfectly round, and appeared almost artificial. The Raven pilot thought it was caused by methane gas, and quickly flew away for fear of his vehicle going down. Baird, and perhaps Marcus, thought differently. Baird thought it was the Locust, although he didn't know how they had accomplished such a feat. It would later be discovered that the actions of the Rift Worm were responsible.
The Tollen Town Center was one of the few districts of the city that survived the sinking, and by 41 A.E. its ruins were occupied by the Swarm. JD Fenix and Kait Diaz fought through the Town Center en route to Tollen Dam while piloting DB Industries mechs, and were supported by KR Three-Seven.