Mexican Culture: Xochicalco's Engineers and Scientists

Our friend from Cuernavaca took us to visit the archaeological site of Xochicalco—“In the place of the house of the flowers”—located about 38 kilometers from Cuernavaca on the Cuernavaca-Acapulco Highway, which runs straight across a broad flat plain rimmed by cerros (hills).

Coincidentally or not, as we approached the exit, my friend pointed out numerous puestos (farm stands) selling…roses! Generous bunches of roses (perhaps two dozen per bunch) were neatly stacked almost a meter high on counters. Each grower had a basic color—red or orange—with subtle variations on that color. The stacks of these subtly different shades of roses made a dramatic and beautiful display.

Xochicalco

Declared a UNESCO World Heritage Site in 1999, Xochicalco gained dominance as a Mesoamerican city-state in the political and economic power vacuum created by the fall of Teotihuacan, the dominant city-state in what is now central Mexico during the Classical Period (150-650 CE).

The fall of Teotihuacan created such political, economic and social instability that Mesoamerican city-states, including the Xochicalca people, were forced to develop their own defenses. The height of Xochicalco’s power and influence was achieved during the Epiclassical or Late Classic period from 650 to 900 CE. Its reign was followed by that of  Tula, which is north of present-day Mexico City.

GoogleMap of Xochicalco, Archaeological Site near Cuernavaca, Morelos,
which flourished from 650-900 CE 

As we arrive at the site, we enlist the forces of a local guide, Javier, who has been guiding tours at this site for twenty years and has studied at the University of San Diego. The description that follows makes use of what Javier told us and what I came upon by researching Xochicalco on the Internet—especially information provided by INAH (Instituto Nacional de Antropología e Historia). 

Although the ethnic origin of Xochicalco’s inhabitants is unknown, their knowledge and experience was highly advanced and has achieved world-wide recognition. As the daughter of a civil engineer, the engineering and scientific achievements of the Mesoamericans intrigue me. This first Xochicalco post focuses on those feats. 

Strategic Site Construction

Not only did the Xochicalca rulers site their city strategically on top of a mountain—more accurately, atop a series of hilltops—they also developed a complete urban plan to achieve their strategic vision. The plan called for modifications to join together these hilltops in order to create the fortress-city of Xochicalco in a way that also realized their military and commercial strategy.

Over two centuries (700-900 CE), Xochicalco’s ruler-engineers designed and constructed an easy-to-defend urban site that at the same time assured strategic control over a broad territory of critical trade routes that ran across the plain—just as the modern highway does today.

Our young friend—Master of the Universe—standing at one corner 

of the Grand Plaza overlooking the plain controlled by Xochicalco over a thousand years ago. 

Note one of the lower plazas below

The similarity of this strategy to the one employed at Monte Albán in Oaxaca is noteworthy. Monte Albán’s rulers leveled a hilltop at the junction of two important valleys to create an urban religious and military center that also controlled critical trade routes in those valleys.

Looking out over the valleys from Xochicalco. 

Notice the terraces in the left foreground.

Back-filled Retaining Walls

At Xochicalco, the urban center was constructed atop a series of hills rising 130-meters (426.6 feet) above the surrounding plain (Elevation: 1548 meters, 4856 feet). The hills were joined together by the construction of retaining walls back-filled in a way that formed immense terraces that give the site the appearance of the base of a pyramid of geological dimensions. Joined to these terraces was a system of moats or pits, walls and other defensive elements that permitted the Xochicalcas to prevail over possible attackers. 

Terraced Retaining Walls

At the highest level was a large, level space on which were constructed the grand plaza with public and religious buildings. Adjoining these buildings were luxurious residences for members of the governing, religious and military classes. Lower terraces provided houses and workplaces for the common people. 

Engineering Feat: Water System

An important feature of Xochicalco is the water system for capturing and storing rainwater in large, covered cisterns. Our guide, Javier, explained that water flowing off roofs of the large buildings on the highest level was captured and stored in cisterns for use during the seven dry months each year.

During the dry season, water from these cisterns was piped down to people living on the lower terraces. The water delivery system hence used gravitational pull to deliver the water. The system itself was built using ‘pre-constructed’ tubes that workers assembled in a way similar to techniques used today.

By way of contrast, the years 700 to 900 CE are known today as the Middle Ages—part of the so-called 'Dark Ages'—in Europe that followed the fall of the Roman Empire. During this period European urban residents got water from wells or directly from rivers and lakes. This water was often contaminated due to the close proximity of work and living spaces.

Observatory for Studying the Sun

The numerous caves found on the sides of the hill are not natural. They were excavated by the Xochicalcas in order to obtain construction materials. But many caves served several purposes. This is true, for example, of the cave used as an Observatory for studying and tracking the movement of the sun.

An underground passageway leads to a large chamber fitted with a ‘chimney’. From the base to the surface of the ‘chimney’ measures 8.7 meters (28.5 feet). The mouth of the flue is hexagonal.

Hexagonal Mouth of the Chimney Shaft

The flue is slightly inclined so the sun’s rays can penetrate. The cave is stuccoed and painted black (signifying west), yellow (signifying south) and red (signifying east).  FYI - White signifies north, and green signifies center. 

Sun's rays falling on the floor of the Observatory

The floor was decorated ceremonially and religiously to receive the sun's ray. For a period of 105 days—that is, from April 30 to August 15—as the sun travels northward toward the Tropic of Cancer and then returns, its rays penetrate down the chimney shaft and onto the cave's floor.

Twice each year the sun reaches its zenith, directly overhead. These zeniths occur, respectively, on May 14/15 and July 28/29. At these astronomical mid-days, a very strong ray of sunlight passes through the narrow chimney shaft in the ceiling of the observatory to the cave's floor. Religious ceremonies were held in the cave to mark this solar event. 

At the Zenith, the Sun's rays are vertical

It is said that when you place your arm through this ray of light, you can see your skeleton like an X-ray on the floor of the cave, but actually what you see is an optical illusion created by the umbra and pre-umbra of your own shadow.

We weren't able to visit the Observatory, which is currently closed to the public while conservation work is completed. Certainly, the solar eclipse that occurred in 743 C.E. was visible from Xochicalco.

Catching my Breath

Believe it or not, we learned all of the above information in about the first 30-45 minutes of our two-hour tour!  The engineering feats are impressive, but so is the ability of Xochicalco's ruling elite to organize and administer a city-state of this size.

The next post will discuss the myths and symbols of Xochicalco, which is dedicated to Quetzalcóatl (Plumed Serpent). Stay tuned!