For most people, the name "Mark Twain" is virtually synonymous with the life along the Mississippi River immortalized in the author's writing. Clemens first signed his writing with the name in February 1863, as a newspaper reporter in Nevada. "Mark Twain" (meaning "Mark number two") was a Mississippi River term: the second mark on the line that measured depth signified two fathoms, or twelve feet—safe depth for the steamboat. In 1857, at the age of twenty-one, he became a "cub" steamboat pilot. The Civil War ended that career four years later by halting all river traffic. Although Clemens never again lived in the Mississippi valley, he returned to the river in his writing throughout his life. And he visited a number of times, most notably in 1882 as he prepared to write Life on the Mississippi, his fullest and most autobiographical account of the region and its inhabitants, and again in 1902 when he made his final visit to the scenes of his childhood.r.