Hannibal, Missouri, on the Mississippi River was the home of Samuel Clemens from age 4 to 17 after the Clemens family moved to the riverfront town in 1839. The area's limestone geology and many bluffs made caves common, and in 1832 a large cave was discovered and named Simms Cave, becoming a source of fascination for local children. The cave took on greater mystique when an eccentric doctor used it as a tomb for his young daughter's body, placing her in a copper cylinder in the belief that the cave's dry air would mummify her. In his autobiography, Clemens recounts skipping school one day to visit the cave and putting a bat in his pocket to keep as a pet before returning home, only for his mother to find it in his jacket. Writing as Mark Twain, Clemens portrayed Tom and Becky's adventure lost in McDougal's Cave, clearly drawing on his memories of Simms Cave. Today, Mark Twain Cave is a popular tourist site, and a large bur oak at its entrance is known as the Mark Twain Cave Bur Oak.