that three of the region's largest and most important ancient centers were linked by a 450-mile meridian line--Chaco Canyon, in New Mexico; Aztec Ruins, 55 miles due north near the Colorado state line; and Casas Grandes, 390 miles due south in Chihuahua, Mexico. Chaco and Aztec were also connected along the meridian by a road known today as the Great North Road (see ARCHAEOLOGY, January/February 1994). Tree-ring dates indicate that Chaco was occupied mainly from A.D. 850 to 1125 (after which its population was greatly diminished), Aztec from 1110 to 1275, and Casas Grandes from 1250 to 1500. As Chaco was dying out a new center was being created on the same meridian at Aztec. In commemoration of the earlier site, the new one was connected to it by the Great North Road. When Aztec collapsed and the Four Corners area was abandoned, Casas Grandes arose due south of Chaco. While no road has yet been found between Chaco and Casas Grandes (efforts are under way to survey the corridor by aerial and satellite photography), the alignment of the two centers no doubt reflects ideological and symbolic connections. The area covered by the Chaco-Aztec-Casas Grandes meridian and adjacent sites is more than 100,000 square miles--1,000 times the typical survey area around a Southwestern archaeological site. The existence of a political system encompassing so great an area will require the review and revision of almost every aspect of Southwestern prehistory, but its full meaning is not yet clear. 11 Thus the