to include central plazas and earthen mounds, occasionally enhanced by masonry. For instance, the site of La Blanca featured a central mound more than seventy-five feet tall and contained a masonry fragment strongly resembling a head in the distinctive Olmec style. Carved stone stele also began to appear during this period, adorned with portraits of rulers but still devoid of writing. Warfare appears to have intensified during this period, as evidenced by advanced weaponry, rulers beginning to be portrayed as warriors, and the appearance of mass graves and decapitated skeletons. Beginning around 900 BC, the Pacific coastal region fell under the dominance of the La Blanca statelet, which collapsed around 600BC, to be replaced by a polity centered on the El Ujuxte site. Another early statelet was probably based at the site of Chalchuapa, a town with extensive earthen mounds arranged around several plazas. However, it was likely ruled by the first true Maya city-state, Kaminaljuyu. Lying within modern-day Guatemala City on the shores of Lake Miraflores, Kaminaljuyu developed a powerful government structure that organized massive irrigation campaigns and built numerous intricately designed stone monuments to its rulers. These monuments clearly depict war captives and often show the rulers holding weapons, indicating the Kaminaljuyu polity engaged in active warfare, dominating the Guatemalan highlands for centuries. Kaminaljuyu's main export was the essential resource obsidian, a beautiful volcanic glass that easily fractured into sharp edges, providing arrowheads, knives, and other weapons as well as prestige goods like mirrors. Although it is difficult to firmly identify the ethnicity of a people from meager archeological remains, it appears that during this period the Maya began a systematic northward expansion, occupying the Petén Basin where such cities as El Mirador, Tikal, Calakmul, and Tayasal would be built. The dominant site of these early colonists was Nakbe in the El Mirador basin, where the first attested Maya ballcourt and sacbeob (stone causeways) were built. The rulers of Nakbe constructed several stone platforms and erected intricately carved stone and stucco monuments. During this period, the Olmec culture reached its zenith, centered on the capital of La Venta in modern-day Tabasco near the early Maya centers. Speakers of a Mixe–Zoquean language, the Olmec are generally recognized as the first true civilization in the Americas. Their capital city of La Venta contains extensive earthworks and stone monuments, including several of the distinctive Olmec stone heads. The Olmec share several