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Roman Church or Solar Observatory?

 Roman Church or Solar Observatory?

In this episode, we’re visiting a most unique building in Rome: an enormous 3rd century public bath dedicated to Emperor Diocletian that later became a church that Michelangelo helped design, and then transformed into a solar observatory.

Welcome to Santa Maria degli Angeli e dei Martiri: a Roman church or a Solar Observatory?




Bonus Feature segment on the official A Road Retraveled Travel App: Michelangelo is famous for designing the dome of St Peter’s, but what did he do to transform these ancient Roman baths into a church? And what were these ancient baths like when they were built? Did Galilelo give his critics an eternal finger, and find out where can you see IT, AND his famous tomb!

Santa Maria degli Angeli e dei Martiri 

The History of the Church

In 1541 Sicilian priest Antonio Lo Duca had a vision of angels inside the ruins of the Baths of Diocletian, which inspired the construction of a church within the tepidarium of the ancient Roman baths themselves and dedicating it to St Mary of the Angels and Christian martyrs, known and unknown. The designs of the church were entrusted to none other than Michelangelo, and although he died a year alter, the designs were completed by the nephew of father Lo Duca.

Santa Maria degli Angeli e dei Martiri

Santa Maria degli Angeli e dei Martiri

Predicting Easter

Now, churches back then had a bit of a problem predicting the exact day of Easter, even after switching from the Julian calendar to the Gregorian calendar in 1582.  To check the accuracy of the Gregorian calendar, by early 1700′s the Church had to go high tech astronomically, which is ironic considering at this point the Church was still advocating geocentrism, or the Earth being the center of the Universe,… and only some 60 years earlier, Galielo died a condemned man accused of heresy by the Roman Inquisition for his heliocentric opinion… Even more ironic, the day I visited St Maria degli Angeli e Martiri, there was an exposition taking place inside the church honoring Galileo, the father of modern physics, and the man persecuted by the Church only to have his sins forgiven 450 years later by Pope John Paul II.

Meridian Lines

Santa Maria degli Angeli e dei Martiri Church, Rome

Santa Maria degli Angeli e dei Martiri Church, Rome

As astronomers struggled with meridian lines and the discrepancies apparent in their observations, they became more and more aware that the Earth indeed revolves around the Sun, and not the other way around.

Given the Church’s need to accurately predict future Easters, and the architectural height and space found inside churches necessary in order to build long meridian lines, it ultimately gave the Catholic hierarchy no choice but to embrace the heliocentric principle they so furiously rejected before.  So during the shift between geocentrism and heliocentrism, Pope Clement XI commissioned a sundial, or meridian line, to be built inside this church.

The reasons behind choosing THIS particular church were the unobstructed exposure to the sun, the building being southerly oriented like all the ancient Roman baths, the tall walls allowed for a long meridian line to more precisely measure the sun’s progress throughout the year, the perfectly constructed vertical walls and horizontal floor,  the ancient building no longer in danger of settling and disturbing the calibration of observational instruments, and of course it would symbolically represent victory of the Christian calendar over the previous pagan calendar. All these elements harmoniously worked together to transform this church into a solar observatory continuously studying the sun with the most precise state of the art instruments in accordance to the best astronomical practice of those times.

The sundial is 45 meters long to better calculate the length of the year, and built along the meridian that crosses Rome from south to north. At solar noon, the sun shines through a small hole in the wall and beams its ray of light on this line each day. At the summer solstice in June the sun appears highest, and the light hits the meridian line at the point closest to the wall. At the winter solstice in December, the ray hits the line at the point furthest from the wall. At either equinox in March or September, the sun beams between the these two extremes. The longer the meridian line, the more accurately the observer can calculate the length of the year.

But how do we know this sundial is properly calibrated and nothing has shifted over time? To confirm that the verticality of the wall is perfect, a plumb is used. To verify the perfect horizontality of the floor, a tube of water was placed to the left and right of the meridian line, and checked to make sure the liquid is level. In over 1500 years, the walls and floor have not shifted a single millimeter, thanks to the skillful ancient Roman architects who built these baths.

The meridian line is made of bronze and marble. The marble astrological signs are fine example of veneered marquetry inspired in 16th century Florence.

Santa Maria degli Angeli e dei Martiri Church in Rome

Santa Maria degli Angeli e dei Martiri Church in Rome

 And this is how a small hole in the exalted roofs of churches shed light not only upon the mysteries of the calendar; but also illuminated the path to scientific enlightenment.

By 1758 the scientific studies and writings of Galielo, and Copernicus before him, began to see the light of day when they were removed from the Church’s Index of Forbidden Books, laying the foundation for modern science.

So next time you find yourself at the Termini Station in Rome, walk over to Piazza della Repubblica and visit this enormous 3rd century public baths dedicated to Emperor Diocletian that later became a church, and then transformed into a solar observatory.


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