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 in the Americas to develop a sophisticated style of stone sculpture. In the first decade of the 21st century evidence emerged of Olmec writing, with the earliest examples of Olmec hieroglyphs dating to around 650 BC. Examples of script have been found on roller stamps and stone artefacts; the texts are short and have been partially deciphered based on their similarity to other Mesoamerican scripts. The evidence of complex society developing in the Olmec heartland has led to the Olmecs being regarded as the "Mother Culture" of Mesoamerica, although this concept remains controversial. Some of the Olmecs' rulers seem to