It is unknown when Lassen was founded, but it enjoyed independence for a certain time, one of its lords notably marrying Celes, a princess of Dipan and a famous general, at some point between 576 C.C. and 581 C.C. However, in 581 C.C., the Rosetta Dynasty invaded the town, sparking the Year-Long War. A rebellion, led by Farant, countered the invasion, and although Farant himself was killed, the town was presumably liberated upon Rosetta's defeat. About 100 years later, Tyrith, the daughter of a Lassen merchant, rose to prominence as a warrior, claiming that she was descended from Celes herself. She allied herself with Arkdain to oppose the newly-created Villnore, but was eventually killed in battle in 659 C.C. However, the town seems to have maintained its independence since then.
It is also unknown when slave-trading was introduced to Lassen, but, at the time of Valkyrie Profile, it appears to be an accepted norm, as the town holds its own slave auctions.
- Belenus can be recruited in Lassen in Chapter 1, even though he is originally from Gerabellum.
- Badrach can be seen visiting the town during a flashback in his recruitment sequence.
- The name of the town could be derived from the German verb lassen (to allow, to permit) , which could be a reference to its tolerance of slave trade.