The cosmic phenomenon that gave rise to Roman Zaragoza and that can be seen this Saturday

There was a time when Zaragoza was not Zaragoza but Caesaraugusta . This ancient Roman city was structured around two main streets: the cardo and the decumanus. Two streets that were not chosen by chance, but have their origin in the winter solstice. A phenomenon that returns this Saturday from 8.30, a key moment in the ancient Roman calendar.

And that day and time a very particular astronomical phenomenon occurs: the alignment of the sun’s rays with Zaragoza’s Calle Mayor, an event that commemorates the winter solstice, but also the founding of the city, and which attracts more spectators every year. So much so that it is now known as Zaragoza’s Manhattanhenge.

When the Romans designed Caesaraugusta two thousand years ago, they did so by looking at the sky and projecting their shadows to determine the exact location where this cosmic prodigy would occur so that the sun would symbolically fertilize the earth. This gave rise to the cardo maximus and decumanus maximus, the main streets around which the city would be structured.

This commemoration will take place this Saturday, December 21, starting at 8:30 a.m. and has been organized by the Museums of the Caesaraugusta Route. After seeing this phenomenon, different activities will take place at the Caesaraugusta Theatre Museum. At 10:00 a.m. there will be a talk about the Roman calendar led by Guillermo Fatás. At 11:30 a.m. there will be a live recording of the podcast “Roman Stories” with Néstor Marqués as a guest. There will be talk about the Cantabrian Wars. Admission is free until full capacity is reached.

THE ORIGIN OF THE FOUNDATION OF CAESARAUGUSTA

The importance that Roman beliefs gave to official names invites us to think that Caesaraugusta was founded on a date coinciding with some Augustan event and in its honour, which could have been its fiftieth birthday: either on 23 September 13 BC (autumn equinox, beginning of the zodiacal celestial sign of Libra), or on 23 December 14 BC (winter solstice, beginning of the sign of Capricorn), the day on which, according to Roman belief, Octavius ​​was conceived. Another complementary argument is that the orientation that must technically be given to its axes so that they were in harmony with the cosmos was precisely that which occurred on the winter solstice, which is 13 degrees of deviation with respect to the astronomical North.

The plan of the colony reflected an organisation similar to a military camp with a Hippodamian layout, that is, planned using perpendicular and parallel streets. The main roads of Roman cities were two roads perpendicular to each other, called the cardo maximus (north-south orientation) and the decumanus maximus (east-west). The rest of the streets were laid out parallel to the cardo and the decumanus maximus, forming an orthogonal, network or grid structure.

Caesar Augusta’s main road, the Decumanus Maximus, was supposedly laid out with the orientation of the rising and setting sun on the day of his deductio (23 December 14 BC). The Cardo Maximus was laid out with a north-south orientation.