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
Olmec colossal heads were presumably widely available to the population. Together with these, of particular relevance to the colossal heads are the "Olmec-style masks" in stone, so called because none have yet been excavated in circumstances that allow the proper archaeological identification of an Olmec context. These evocative stone face masks present both similarities and differences to the colossal heads. Two thirds of Olmec monumental sculpture represents the human form, and the colossal heads fall within this major theme of Olmec art. The colossal heads cannot be precisely dated. However, the San Lorenzo heads were buried by 900 BC, indicating that their period