Olmec colossal heads by Matthew Stirling in 1938 spurred the first archaeological investigations of Olmec culture. Seventeen confirmed examples are known from four sites within the Olmec heartland on the Gulf Coast of Mexico. Most colossal heads were sculpted from spherical boulders but two from San Lorenzo Tenochtitlán were re-carved from massive stone thrones. An additional monument, at Takalik Abaj in Guatemala, is a throne that may have been carved from a colossal head. This is the only known example from outside the Olmec heartland. Dating the monuments remains difficult because of the movement of many from their original contexts prior to archaeological
Epi-Olmec culture centers though neither would reach the size and importance of the great Olmec cities before them nor El Tajín after them. Other Epi-Olmec sites of note include El Mesón, Lerdo de Tejada, La Mojarra, Bezuapan, and Chuniapan de Abajo. The rise of the Epi-Olmec culture on the western edge of the Olmec heartland coincides with the depopulation of the eastern half of the Olmec heartland and the decline of the Olmec culture in general. The Epi-Olmec culture represented a gradual transformation of, rather than a sharp break with, the Olmec culture. Many Olmec motifs, for example, were employed by its