[4] The centuries of agricultural village life had begun to form the beginnings of a complex society: Prestige goods such as obsidian mirrors and jade mosaics began to appear, increasing the demand for more extensive trade.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.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.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.