COLLINSVILLE, Ill. (AP) — Portions of the Cahokia Mounds State Historic Site in southern Illinois will close March 1 as work begins on a $5 million improvement project. The Illinois Department of Natural Resources says the work is expected to take about one year. It will include replacing the roof, lighting and fire suppression and security systems within the center. Superintendent Lori Belknap says some of the work was last done in 1988. The 2,200-acre site near Collinsville, about 12 miles east of St. Louis, contains remains of the most sophisticated prehistoric native civilization north of Mexico.