El Castillo, Chichen Itza

Stand still for a moment and feel the heat rise from the ground. The grass of the Great Plaza is short and dry, and the limestone underfoot is pale, almost white, in the Yucatán sun. Ahead of you, a pyramid of grey stone climbs in steep, even steps toward a small temple at the top. Somewhere behind you, a vendor blows a clay whistle, and it gives a low growl like a jaguar. This is El Castillo, the heart of Chichen Itza.

The name El Castillo means "the castle" in Spanish. Spanish newcomers gave it that name in the sixteenth century, because to them it looked like a fortress. But this was never a castle. The Maya built it as a temple to Kukulcán, the feathered serpent. In central Mexico, people knew the same god as Quetzalcoatl. So when you hear archaeologists call it the Temple of Kukulcán, they mean this same building. It is a sacred monument, not a military one.

Think for a moment about where you are standing. The Yucatán Peninsula is a flat shelf of limestone. It has almost no rivers on the surface. Instead, water collects underground and appears through sinkholes called cenotes. The name Chichen Itza is usually translated as "at the mouth of the well of the Itza". Water shaped this city. It decided where people could live, where they prayed, and which places they treated as holy. That fact will matter again before this guide ends.

Now look closely at the pyramid itself. It rises in nine stacked terraces, each one a little smaller than the one below. A staircase climbs each of the four sides, so the building faces all four directions. Together with the temple, the structure stands roughly thirty metres tall. It was most likely built sometime between the ninth and twelfth centuries, during the period when Chichen Itza was one of the most powerful cities in the Maya world.

Here is the first surprise. This pyramid is a calendar made of stone. Each of the four staircases has 91 steps. Multiply 91 by four, and you get 364. Add the single platform at the top, and the total is 365, the number of days in a solar year. Scholars also point to the terraces. The stairways split each side into eighteen sections, which match the eighteen months of the Maya solar calendar. The Maya did not treat time as abstract. They built it.

Walk around to the north side. At the base of the north staircase, two large carved serpent heads rest on the ground, their mouths open. These are the heads of Kukulcán. Now picture the late afternoon around the spring and autumn equinoxes, in March and September. As the sun drops, the stepped corners of the pyramid throw a line of triangular shadows onto the side of the staircase. The shadows form a long, wavy body that seems to slide down toward the stone head.

Thousands of people gather on the plaza to watch that shadow serpent. Whether the Maya designed the effect on purpose is still debated. Some researchers believe it was deliberate. Others think it may be a happy result of the building's orientation. Either way, the event connects people today with the people who stood here centuries ago, looking at the same stone and the same light. The serpent appears for only a short time, and then the sun goes down.

Here is the second surprise, and it is a sound. Stand in front of the main staircase, some distance back, and clap your hands once, sharply. Listen. The echo that returns from the steps does not sound like a clap. It comes back as a chirp, a little like a bird call. Acoustic researchers have compared it to the call of the quetzal, a bird sacred to the Maya. Nobody can say for certain that this was intended. But try it, and you will hear why people wonder.

The pyramid you see is not the only one here. In the 1930s, Mexican archaeologists tunnelled into El Castillo and found an older, smaller pyramid hidden inside. In its temple they found a Chac Mool, a reclining stone figure that holds a bowl on its stomach. They also found a throne carved in the shape of a jaguar, painted red and set with pieces of jade. Later studies have suggested an even smaller and older structure inside that one. The building grew in layers, like a nesting doll.

There is more below the ground, too. In recent years, researchers used scanning techniques that measure how electricity moves through rock and soil. Their results suggest that El Castillo may stand above a cenote, a natural water chamber in the limestone. If that is true, the builders may have placed their great temple directly over sacred water. Remember the city's name, the mouth of the well. The pyramid may connect the sky, the earth, and the water below in a single spot.

For many decades, visitors climbed the steep steps to the temple at the top. That is no longer allowed. Climbing was stopped in the 2000s, to protect the stone and to protect people after a fatal fall. Today you enjoy the pyramid from the ground, and that is not a loss. From the plaza, you see the whole shape at once, with its four faces and its sharp edges against the sky. Chichen Itza became a UNESCO World Heritage Site in 1988.

As you look around the plaza, notice how El Castillo sits in a wide open space. To one side is the Great Ball Court, with its tall walls and stone rings. To another is the Temple of the Warriors, lined with carved columns. A raised white road once ran north from here toward the Sacred Cenote, where offerings were thrown into the water. The pyramid was the centre of this whole arrangement. Everything else points back to it.

Before you walk on, look at El Castillo one more time. Look at the steps, worn smooth along the edges. Look at the shadows sitting in each corner of the terraces, and the small dark doorway of the temple at the top. Listen to the vendors, the footsteps on the dry grass, the cry of a bird in the trees at the edge of the plaza. The Maya built this pyramid to count the days. Today, it is counting one more.