The Marsh System was a star system just outside the border of the Silesian Confederacy. It was the home of the Republic of Sidemore, and after the establishment of Sidemore Station was used by the Royal Manticoran Navy as a staging area for anti-piracy campaigns and convoy escort patrols in the Confederacy.
It contained a single G6 star. (HH6)
- Sidemore Station (RMN Naval base)
- First Battle of Marsh – Captain Honor Harrington destroyed Andre Warnecke's privateer squadron, which had briefly taken over the Republic of Sidemore. (HH6)
- Second Battle of Marsh 1920 PD – A Havenite fleet attempted to destroy the RMN forces at Sidemore as part of Operation Thunderbolt, but was repulsed. (HH10)