Olmec Civilization

The ancient Olmec civilization is considered to be one of the greatest Mesoamerican civilizations. This civilization came and went way before the Aztecs even came, and yet they still have left a clear mark on the people of Mexico, and far more!
Olmec was centered  in stunning San Lorenzo Tenochtitlan, around the Gulf of Mexico, which at the time happened to be the largest city in Mesoamerica due to trade. It was believed to be a religious and political place that housed thousands and created and used an elaborate water and drainage system.  The city is often remembered because of the gigantic stone heads that have been found here. The Olmec's carved their carvings with Jade, stone, and basalt from volcanoes.
It's believed that they were early adopters of the complex religious system that the Mayans and the Aztecs would used. Temple mounds, a variety of gods, and possibly even human sacrifice were used by the Olmec civilization. The calendar used for centuries in Mexico may also have originated with the Olmec's. Their astronomy was also carried over to many society's to come. They were probably obsessed with timing of certain religious rituals, as the Mayans and Aztec were also.