The first significant civilization which developed in Mesoamerica was that of the Olmecs. There culture was developed between 1500 and 100 BC. May the most famous Olmec art are the gigantic helmeted heads. The heads were carved from single blocks or boulders of volcanic basalt. The largest weighs of the olmec-heads weight around 40 tons, the smaller ones around 20 tons. The Olmecs may have been the first civilization in the Western Hemisphere which developed a writing system.