Eldean Bridge, built in 1860, is the only covered bridge left of about 30 that once crossed Miami County streams, one of Ohio's oldest covered bridges, the state's second longest at 222 feet, the longest Long Truss in existence, and one of the finest surviving examples of Stephen Long's invention. Early farmers used it to carry grain to Allen's Mill, later called the Eldean Mill, west of the bridge, and it carried Eldean Road until it was bypassed in 1963. In 1860 the Miami County Commissioners hired brothers James and William Hamilton to build it, paying $1,337 for the stone substructure and $2,632 for the wooden spans, and required use of a Long Truss, named for its inventor Stephen Long rather than the bridge's length. Its white pine timbers, not native to the area, were cut in Michigan and floated to the site on the nearby Miami and Erie Canal, while stones for the abutments and pier probably came from a quarry the Hamiltons owned near Piqua. Over the years decayed timbers were reinforced and the bridge was raised 15 inches to better clear floods, but its appearance and structural behavior have changed little since construction. Stephen H. Long was an explorer, engineer, teacher, and military officer who led the country's third great exploration party west of the Mississippi after those of Lewis and Clark and Zebulon Pike, explored Minnesota in 1817 and surveyed its boundary with Canada, helped design the nation's first railroads between 1827 and 1839 and developed their initial engineering standards, taught at West Point, commanded the Corps of Topographical Engineers, and in 1830 patented the nation's first scientifically designed bridge truss. His Long Truss, developed from his railroad work in the 1820s, was the first patented truss made of large rectangular panels crossed by diagonal timbers for rigidity, with joints tightened by wedges; although he could not calculate timber stresses, he understood the function of each member, and the practical form he created became the basis for many later variations and improvements, including the more common Howe Truss, which uses iron rods instead of timber vertical members. Eldean Bridge closely follows Long's 1830 patent, though it never had the end props or midspan peak shown in the patent, and it was repaired and restored in 2005 by Miami County with federal preservation and transportation funding along with local bridge funds.