The single riderless horse that follows a caisson with boots reversed in the stirrups is called the "caparisoned horse" in reference to its ornamental coverings. The custom is believed to date back to the time of Genghis Khan, when a horse was sacrificed to serve the fallen warrior in the next world. The caparisoned horse later came to symbolize a warrior who would ride no more.
By tradition in military funeral honors, a caparisoned horse follows the casket of an Army or Marine Corps officer who was a colonel or above. It also follows the casket of a president by virtue of having been the nation's military commander in chief. Abraham Lincoln was the first U.S. president to be honored with a caparisoned horse at his funeral.