Teotihuacan

Start with the ground under your feet. It is dry, pale and dusty, and it crunches softly as you walk. The air is thin up here on the high plateau, and the sun feels closer than it should. Somewhere nearby a vendor blows into a small clay whistle shaped like a jaguar. The sound is a low, rough growl that rolls across the open stone. In front of you, a long straight avenue runs into the distance, lined with low platforms and stairways. At the far end, a pyramid rises against a mountain.

This is Teotihuacan, about an hour's drive northeast of modern Mexico City. For several centuries in the first millennium of our era, this was one of the largest cities in the world. Scholars estimate that perhaps one hundred thousand people lived here at its height, possibly more. It was larger than most European cities of the same period. And yet, here is the first surprise. We do not know what its own people called it. We do not even know which language they spoke.

The name you hear today came much later. When the Aztecs arrived in this valley, the city had already been empty for hundreds of years. They walked through these same ruins and saw something too vast to have been built by ordinary people. They called it Teotihuacan, usually translated as the place where the gods were created, or the place where men became gods. Their legends said the sun and the moon were born here. The Aztecs also named the avenue you are looking at. They called it the Avenue of the Dead.

That name is a misunderstanding — a beautiful one. The Aztecs believed the low mounds along the avenue were tombs. In fact, most of them were temple platforms and elite residences. The avenue runs for several kilometres, and it is not aligned exactly to true north. It is turned slightly east. Many researchers believe this angle follows the movement of the sun and certain stars across the sky. The whole city was laid out on a single, deliberate grid around this line.

Look at the sides of the platforms around you. You will see a repeating pattern. A sloping wall rises from the ground, and on top of it sits a flat, vertical panel with a frame. Archaeologists call this talud-tablero, which simply means slope and panel. It was the signature look of Teotihuacan. Once you know it, you will notice it everywhere here. Copies of this style also appear at sites far away in Mesoamerica, including Maya cities, which shows how far this city's influence reached.

Now turn toward the largest structure on the avenue — the Pyramid of the Sun. It is one of the biggest pyramids ever built in the Americas. It was made mostly of earth and rubble, then faced with stone and covered in plaster. In its time, that plaster was probably painted, most likely in strong reds. Imagine it not as grey stone, but as a bright, smooth mountain shining in the sun. That is closer to what the people of this city saw every day.

Here is the second surprise. Beneath the Pyramid of the Sun, archaeologists found a tunnel cut into the rock, leading to a chamber deep under the centre. Caves held deep meaning in Mesoamerican belief. They were often seen as entrances to the underworld, or as places of origin. It seems the builders chose this exact spot because of what lay below it. The pyramid you see was built on top of something already sacred. The shape you see today also owes something to an early twentieth century restoration, which removed some of the original outer layers.

Follow the avenue north and it ends at the Pyramid of the Moon. Stand in the plaza in front of it and look past its summit. Behind it rises a mountain called Cerro Gordo. The pyramid's outline repeats the shape of the mountain almost exactly. This is no accident. The builders placed their monument so that stone and landscape would read as one. Inside this pyramid, excavations found burials with offerings of animals and people, which tells us that ritual sacrifice was part of life here.

Just off the plaza of the Moon is a building called the Palace of Quetzalpapalotl. That name means quetzal butterfly, after the bright green bird and the insect carved into its stone pillars. Walk into its courtyard and look closely at the columns. You will see carved birds, some shown from the front and some in profile. Small pieces of shiny stone once filled their eyes. The roof is a modern reconstruction, but the shade inside lets you feel how these rooms worked as cool, quiet spaces.

At the southern end of the avenue lies a huge enclosed square the Spanish called the Ciudadela, meaning the citadel. Inside it sits the Temple of the Feathered Serpent. Its walls carry carved serpent heads with ruffs of feathers around their necks. Between them are other heads, square and staring, which scholars still debate. Some see a rain god. Others see a war serpent's headdress. Traces of the original paint survive in places. Beneath this temple, too, archaeologists found a long tunnel in the early 2000s, filled with offerings, including traces of liquid mercury.

Teotihuacan was not only temples. Most people lived in large stone apartment compounds, each housing many families. Some neighbourhoods held people who came from other regions, including Oaxaca and the Maya lowlands. The city was a working place. Workshops shaped obsidian, a sharp black volcanic glass, into blades and tools that travelled across Mesoamerica. Inside some compounds, walls still carry painted murals of gods, jaguars, water and flowering trees. These paintings give us the closest view we have of how these people saw their world.

Then, sometime around the sixth century, the city's heart burned. Fire swept through the temples and elite buildings along the avenue. Whether this was an uprising, an invasion or something else, no one knows for certain. Over the following generations the population drained away. The great city did not vanish overnight, but it never recovered its power. By the time the Aztecs walked here, grass and soil covered much of what you see now.

The site became a UNESCO World Heritage Site in 1987, and excavation still continues today. Every few years, new finds change the story a little. That is part of the pleasure of standing here. This is not a finished chapter in a textbook. It is an open question, laid out in stone, under a very wide sky. Even the experts are still walking these same paths, looking for answers.

So take a moment before you move on. Feel the warm stone under your hand. Listen to the jaguar whistles, the wind, the footsteps of other visitors on the avenue. Look once more along that long, slightly turned line toward the Pyramid of the Moon and the mountain behind it. The people who planned this view are gone, and their names are lost. But the line they drew across this valley is still here — and you are standing on it.