To the west was the Great Belt (Storebælt), the strait that separates Zealand and the island of Funen peninsula.

Korsør was likely built in the 1100-1300s, and was granted the status of a market town (Danish: Købstad) in 1425 - possibly earlier.

Korsør became a prominent transit town between Zealand, Funen and Langeland.

The remaining population lived in rural areas, as well as the two larger settlements of Forlev and Svenstrup.

Until the construction of the Great Belt Bridge Korsør was largely a transit town.