Catequilla (Cerro Catequilla), is an ancient pre-Hispanic mountain observatory located on a ridge in the Pomasqui Valley about 26 kilometers north of Quito, Ecuador. Built by the indigenous Quitu-Cara culture, its summit sits precisely at latitude 0°0′0″, where ancient peoples aligned stone structures and vertical markers to track celestial events.Key details about Catequilla include:True Equator Alignment: Verified by modern GPS to sit directly on the zero-latitude line, unlike the more famous tourist monument nearby.Ancient Observatory: Used by pre-Incan and later Incan civilizations to observe the sun, moon, and horizon equinoxes/solstices.Archaeological Remains: Features low stone circular structures, wall remnants, and foundational archaeological touchstones.

The current famous 30-meter-tall (98 ft) Mitad del Mundo monument near Quito, Ecuador, was constructed between 1979 and 1982. It replaced an older, smaller stone marker that had been built on the site in 1936.History of the Monuments1936 Marker: The government of Ecuador built the first small monument under the direction of geographer Luis Tufiño.1979–1982 Structure: The large current tower and the surrounding Ciudad Mitad del Mundo complex were built to honor the 18th-century French Geodesic Mission.Fun FactModern GPS measurements show that the famous 1979 monument is actually located a couple of hundred meters away from the true, exact equator line.

French Geodesic Mission to the Equator

The Spanish-French Geodesic Mission (French: Expédition géodésique française en Équateur), also called the French Geodesic Mission to Peru, was an 18th-century expedition to what is now Ecuador carried out for the purpose of performing an arc measurement, measuring the length of a degree of latitude near the Equator, by which the Earth's radius can be inferred. The mission was one of the first geodesic (or geodetic) missions carried out under modern scientific principles, and the first major international scientific expedition.

Map of the meridian by Jorge Juan and Antonio de Ulloa, showing triangulation across mountains in the Andes near the equator.

Background
In the 18th century, there was significant debate in the scientific community, specifically in the French Academy of Sciences (Académie des sciences), as to whether the circumference of the Earth was greater around the Equator or around the poles. French astronomer Jacques Cassini held to the view that the polar circumference was greater. King Louis XV and the academy sent two expeditions to determine the answer: a northern expedition was sent to the Torne Valley in Lapland, close to the Arctic Circle, with the Swedish physicist Anders Celsius and under the guidance of the French mathematician Pierre Louis Maupertuis. The other mission was sent to Ecuador, at the Equator. Previous accurate measurements had been taken in Paris by Cassini and others.