Hamilton developed as a true Mississippi River town along the Great River Road, where rolling hills and timber along the river first attracted settlers and steamboat traffic became a memorable part of local life, with residents enjoying Sunday picnics on the riverbank and hearing the call of "Mark twain," a steamboat term meaning the river was two fathoms deep and safe to navigate that Samuel Clemens, a licensed steamboat pilot, adopted as his pen name, Mark Twain. Hamilton's reliance on the river is most visibly represented by the Keokuk dam and power plant, constructed between January, 1910 and May, 1913, which help barges and boats navigate safely and provide an important source of clean energy, while the islands, wetlands, and timberland above the dam create year-round wildlife habitat where bald eagles roost in winter and feed on fish in open waters. When completed, the dam spanned nearly one mile and was the second longest in the world; it remains the longest dam on the Mississippi, was designated a National Civil Engineering Landmark in 1989, its Lock 19 is listed on the National Register of Historic Places, and it is the largest privately owned dam and powerhouse on the Mississippi.