Deep in a humid Mexican jungle stands a disembodied stone head over 11 feet tall, weighing as much as a fully loaded airplane. The civilization that placed it there 3,000 years ago had no wheels and no beasts of burden. How?

This episode explores the 17 confirmed Olmec colossal heads — the literal heavy proof of the Americas' first great civilization. We dig into the staggering logistics of moving 40-ton boulders across 90 miles of swamp, the Stone Age carving techniques, and what these fiercely individual faces actually represent.

• How violent volcanic mudflows (lahars) pre-shaped basalt boulders that the Olmecs then floated on hardwood rafts and hauled over earthen causeways.
• The revelation that many heads were re-carved from monumental stone thrones — a literal seat of power transformed into a ruler's face.
• Carv ...