Teotihuacán, much of it was constructed between 100 and 650 AD, thus predating the more famous civilizations that the Spanish encountered. Teotihuacán, in fact, was a ruin when the Mexica were the dominant empire.
This panorama was taken from the second largest pyramid on these grounds, known as the “Pyramid of the Moon.” On the left side of this main footpath is the third-largest pyramid in the world, known as the “Pyramid of the Sun.” (Those at Cheops and Cholula are bigger.) Still, it weighs more than three million tons, and was constructed without the wheel or animal labor. This means that if there were a million people working on the structure, they would each have to move 6,000 pounds of rubble. Yet the population of this town peaked at 175,000 — though they probably used tribute labor from other parts of the empire to help build it. Although this pyramid is known as “of the Sun,” recent evidence indicates that it was actually used to worship the rain god, Tlaloc. (Known by the name of a similar deity worshipped by the Mexica, since the name used at Teotihuacán is not known. Teotihuacanese glyph writing has not been deciphered.) In the picture below, which I took half-way up the pyramid, you can see more evidence of this. People have been leaving notable sacrifices to Tlaloc, though we will have to see if the God of Fresca’s jealousy is needlessly aroused for a lack of contributions.
It is very difficult to imagine Teotihuacan as it was more than 1500 years ago. A pile of rock today, the pyramids would then have been covered in plaster and paint. The Pyramid of the Sun was apparently red. A few segments of mural that have survived. They can be found in a beautiful but out-of-the-way museum, and an impressive original structure that is equally out of the way. (They’re both outside of the official grounds of the archaeological site.) This picture is from the latter site, so you can see both the richness and the limitations of what remains: