http://en.wikipedia.org/wiki/Sherman%27s_neckties
"Sherman's neckties were a phenomenon of the American Civil War. Named after Maj. Gen. William Tecumseh Sherman of the Union Army, Sherman's neckties were railway rails 'destroyed by heating them until they were malleable' and twisting them into loops resembling neckties, often around trees".
In some cases if the Union troops had to quickly move on they would start a bonfire with the railroad ties and other wood, put the railroad rails on top of it, leave and let gravity bend the rails under their own weight. They could be used again but not without some work.