Cave-In-Rock, also known as Murrell's Cave and Potato Cave, is a 17-metre-wide riverside cave located in the town of Cave-in-Rock, State of Illinois, United States.
The cave was formed by wind and water erosion of the limestone bluffs on the Ohio River, caused by glacial meltwater following the Wisconsin Glacial Episode 75,000 to 11,000 years ago.
The first European to document the cave was M. de Lery of France, who in 1729 mapped and named it "caverne dans Le Roc".
In the latter part of the 18th century, the Ohio River became infamous for river piracy, with Cave-In-Rock earning a reputation as the reported hideout of pirate gangs, highwayman and brigands.
River pirates along the Ohio River operated in isolated frontier settlements, which were sparsely populated areas lacking the protection of civil authority and institutions. They used techniques of deception, concealment, ambush, and assaults in open combat near natural obstacles and curiosities.
The cave became associated with Samuel Ross Mason, a former Virginia militia captain on the American western frontier during the American Revolutionary War. Mason was the leader of the Mason Gang, a criminal group of river pirates and highwaymen who raided boats on the lower Ohio River and the Mississippi River.