A gateway from a single stone
The Tiwanaku Sun Gate stands at an altitude of 3,825 meters (12,549 feet) on the high plains of Bolivia. This monumental arch is approximately 3 meters (9.8 feet) tall and 4 meters (13 feet) wide, with an estimated weight of 10 tons. The entire structure was carved from a single block of grey andesite. When European explorers documented the gate in the mid-19th century, they found it lying horizontally with a large crack through its upper right side. Today it stands upright in the Kalasasaya temple enclosure, though this is not believed to be its original location.
The gate's most prominent feature is a bas-relief frieze above the doorway. At its center is a figure widely identified as a principal Tiwanaku deity, possibly a forerunner to the Inca creator god Viracocha. This central figure holds a staff in each hand, and its head is surrounded by 24 rays that some interpret as solar rays. Flanking this deity are 48 smaller, winged figures arranged in three rows. Thirty-two of these attendants have human heads, while the other 16 have avian heads, possibly representing condors. All of the figures appear to be running toward the central deity.
An astronomical calculator
The precise meaning of the Sun Gate's iconography is a subject of scientific debate. The carvings are believed to hold astronomical or astrological significance, possibly functioning as a calendar. Early 20th-century researcher Arthur Posnansky was a prominent proponent of the calendar theory, suggesting that the gate and surrounding structures were part of a large solar observatory.
One interpretation posits that the gate tracks a solar year, but one that does not align with our modern 365-day system. This theory suggests a calendar of 290 days, divided into twelve months of 24 days. The number of attendants and other geometric elements on the frieze are part of this calendrical hypothesis. The 290-day cycle is also notable for its proximity to the average length of human gestation. Other scholars propose that the imagery represents celestial cycles in a more general sense rather than a specific, functional calendar. The central figure is sometimes identified as a weather god, Thunupa, rather than a solar deity, which would give the gate a meteorological rather than purely astronomical function.