Seven earthen forts protected the only exposed area of Camp Nelson along its northern periphery. All were formidable earthworks with breastworks eight to ten feet high. The larger forts, Nelson, Jackson, and Taylor, were 300 to 400 feet wide, while the smaller forts, Hatch, Pope, McKee, and Jones, were 100 to 200 feet wide. The three large forts mounted artillery, and infantry manned the other four. An infantry trench connected all seven forts and allowed soldiers to move safely along the line. The cast-iron Parrott rifle, patented in 1861, was the most common rifled cannon in the Union army, and the thirty-pounder Parrott used at Camp Nelson was a siege or garrison weapon fired through embrasures. In May 1865, Inspector General Officer Maj. Murray Davis wrote that Camp Nelson was protected by the Kentucky River on the south and west and by Hickman Creek on the east, and that forts Taylor, Jackson, and Nelson each mounted six 12-pounder Napoleon guns and one 30-pounder Parrott. He judged the works well constructed and capable of defense against almost any force if properly manned. Lt. Colonel James H. Simpson, chief engineer for the Army of the Ohio, was responsible for the defense of Union installations in his jurisdiction, including Camp Nelson, and Captain Orlando Poe directed the initial phase of constructing its defenses.