In September and October 1868, two notable actions happened with Troops H & I under the command of Brevet Lieutenant Colonel  Louis H. Carpenter. The first was the rescue of Lieutenant Colonel G. A. Forsyth whose small party of 48 white scouts, was attacked and "corralled" by a force of about 700 Native American Indians on a sand island up the North Fork of the Republican River; this action became the Battle of Beecher Island. The second was two weeks after Carpenter had returned to Fort Wallace with the survivors of Forsyth's command. Troops H and I of the 10th Cavalry sallied forth for an escort and supply to the 5th Cavalry near Beaver Creek. Near there Carpenter combined command was attacked by a force of about 500 Indians. After a running fight and defensible stand the "hostiles" retreated. Carpenter would later receive the Medal of Honor for these two actions. For the next eight years, the 10th was stationed at numerous forts throughout Kansas and Indian Territory , including Fort Gibson starting in 1872. They provided guards for workers of the Kansas and Pacific Railroad, strung miles of new telegraph lines, and to a large extent built Fort Sill. Throughout this period, they were constantly patrolling the reservations and engaging "hostiles" in an attempt to prevent Indian raids into Texas.
Question: Who built Fort Sill?
Answer: 10th Cavalry