Teotihuacan becomes the dominant political and economic force of Mesoamerica. Boasting the largest urban population in the region, it controls the nearby and highly important obsidian mines. Teotihuacan apparently sends a military force into the Maya region at the end of the fourth century. The hilltop center of Monte Albán expands to control the Valley of Oaxaca. Farther to the west, in Colima, Nayarit, and Jalisco, lively and elegant ceramic sculptures are placed in shaft tombs. On the Gulf Coast, inheritors of the Olmec tradition develop a still poorly understood hieroglyphic writing distinct from the Maya and Zapotec systems.