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
Mayan languages only past and non-past, while Mam has only future and non-future. Aspect systems are normally more prominent. Mood does not normally form a separate system in Mayan, but is instead intertwined with the tense/aspect system. Kaufman has reconstructed a tense/aspect/mood system for proto-Mayan that includes seven aspects: incompletive, progressive, completive/punctual, imperative, potential/future, optative, and perfective. Mayan languages tend to have a rich set of grammatical voices. Proto-Mayan had at least one passive construction as well as an antipassive rule for downplaying the importance of the agent in relation to the patient. Modern K'iche' has two antipassives: one which ascribes focus