Sunday, July 20, 2008

The Church, Time, and the Meridiana

Laura Bauer
Honors in Rome - Summer 2008

Time is a fickle and fleeting idea, but it is also one that often drives the decisions of important institutions. In this particular instance, time was of the utmost significance to the Catholic Church. The Church wanted to be sure that they celebrated Easter on the correct date, which was very difficult because of the discrepancies that manifested over centuries of compounding incorrect calculations. The focus here is on achieving the beginning of the end of this problem, which finally occurs by the building of a scientific instrument within a pre-existing church. This apparatus is known as a meridiana line, which is used to determine local noon, and if made correctly, it is a more accurate time indicator than clocks. Thus, the Church commissioned one to be built in Santa Maria degli Angeli e dei Martiri, which stands in the Baths of Diocletian, near the present-day Termini station. A brief history of the building of the church will be necessary to understand the later reasons for why this particular church is chosen.

Santa Maria degli Angeli e dei Martiri

The Baths of Diocletian, completed in AD 306 under the reign of Emperor Diocletian, had been sitting in Rome for centuries when it was decided to use them as the site for Santa Maria degli Angeli e dei Martiri. This conversion occurred in 1541, when a Sicilian priest, Antonio del Duca, had a vision that would revive the reverence of the Baths as an important monument of Roman history. He purportedly was visited by angels, who instructed him to convert the Baths of Diocletian into a church that would honor the Virgin Mary (Ackerman 123). Del Duca immediately attempted to have his vision turned into a reality, but the reigning Pope, Paul III, as well as his successor, Julius III, declined his request. Pope Pius IV, however, was excited about this idea, and granted del Duca the right to proceed. Pius did have another reason for acquiescing to del Duca: he had just built a new avenue, Via Pia, in the area next to the Baths, and was busy creating a small shopping area around it. He thought that a new church placed in such a significant Roman ruin would nicely add to his newly revived district.

Another attractive feature of using the Baths as the site of the church was the fact that they were pagan in origin. The construction of Santa Maria degli Angeli was one of the first moves by the papacy in the Counter Reformation, so restructuring a well-known pagan site into a church commemorating the Mother of the Church signified a strong Catholic presence in Rome. Further, it was a poignant move: the Baths of Diocletian were mainly constructed by Catholic slaves, who were, at the time, persecuted by the Roman Empire for their beliefs. Thus, a site once build by the toil of Catholics would now represent their intense faith.

The Sicilian priest also had a plan for how the church should be built. He wanted the great hall of the Baths to be the nave of the church, with a northwest entrance which would open onto the Via Pia. This would have placed the alter on the opposite, southeast end (Ackerman 125). Del Duca’s plan was originally adopted in 1550, and work began on incorporating his vision into the design of the church. However, in the midst of planning, the Carthusians gained control of Santa Maria degli Angeli, and they did not appreciate the openness of del Duca’s plan because it did not allow them enough seclusion, which was an integral part of their particular order. Therefore, an alternate plan was commissioned, and eventually Michelangelo’s design was chosen, partly because he had also designed the Via Pia. Pope Pius IV officially consecrated it as the church and monastery of Santa Maria degli Angeli e dei Martiri (the Church of St. Mary of the Angels and the Martyrs) in 1561 (Ackerman 123).

Michelangelo’s plan was the complete opposite of del Duca’s. His overarching plan was to preserve the original facades and structure of the Baths of Diocletian. Due to this technique, he chose to place the entrance of the church in the rotunda and construct the alter across the great hall in the passage to the frigidarium. This, according to Michelangelo, was the logical place to build the church because the frigidarium was the only room that was large enough and sufficiently devoid of ruins to erect the cloister with the minimum destruction of the site. This plan was well-suited to the Carthusians because it isolated the chancel from the main hall, which would contain the public alters, and thus provided them with the maximum amount of privacy. Michelangelo also was able to build a choir that was isolated from the church because he pursued minimum demolition of existing features of the Baths (Ackerman 126). Michelangelo’s design of the church also allowed the church to be constructed with the maximum amount of symmetry. This architectural practice was a hallmark of Renaissance architecture and thus held more public appeal. In fact, he managed to make every aspect of the church symmetric with respect to the line that connected the main alter and the entrance. Further, he designed the church in the shape of a Greek cross, which bespoke of strong Catholic influence, which the papacy endorsed in its Counter-Reformative struggle against the Protestants.

For many centuries before the building of Santa Maria degli Angeli, the Catholic Church had struggled with its calendar. The transition from lunar to solar months had not been a smooth one, and had left ambiguities as to when the true Christian observance of religious holy days was to take place. The most concerning among these days was Easter. This day is a celebration of the rebirth of Christ and, implicitly, of the hope God represents, which meant that the Church thought observance of it upon the proper day was of utmost importance. Traditionally, the theologians had decreed that “Easter should be celebrated on the Sunday after the first full moon after the vernal equinox” (Heilbron 3). Originally, Catholics had to depend on the rabbis for the correct date of Easter, because it was known that the day Jesus died was the second day of Passover. This holy week was designated by a specific Jewish month and was the celebration of the new spring, occurring in relation to the vernal equinox. The Julian calendar calculated that Christ had died on a Friday, which meant that the first Easter occurred two days after this. The Christians attempted to reconcile the Hebrew lunar calendar with the Juilan solar calendar so that they would not rely on their rival faith to declare the date of Easter.

Unfortunately, reconciling these two calendrical systems with each other to calculate the date of the vernal equinox was very difficult and given to inconsistencies and miscalculations. The Church was very unhappy with the rather gross inconsistencies surrounding the celebration of Easter, because it meant that not only was the correct day not being observed, but also that the power of the Church was not absolute. Their next move was to adopt the Julian solar year of 365.25 days, instead of the odd amalgamation of lunar and solar calendrical systems that was currently used. This caused its own difficulties, as it was tricky to calculate average values of successive vernal equinoxes as well as the average length of a lunar cycle, and so determining when the correct observance of Easter should occur was still a problem. These values were first calculated in the sixth century, and went largely uncontested until the twelfth century, when it was noticed that the vernal equinoxes were not coinciding with their predicted dates.

After this, many different theories attempted to align the calendar into a unified system; all of these agreed that the major issue was the fractional day that the solar year left (365.2422 days). That fraction of a day was always rounded, which led to a compensatory cycle of extra days every few hundred years. However, depending on whether it was rounded up by 0.008 or 0.0075 to one quarter of a day varied both what year was to have days added to it as well as how many days were to be added. Several systems were constructed to deal with this. Unfortunately, by the end of all the mathematics, every system ended up with errors due to rounding or miscalculation. Added on to this difficulty was the emergence of varying church calendars, such as how Britain refrained from adopting the Catholic calendar, which meant it celebrated Easter at a completely different time than the Vatican-decreed date. By the time the Reformation threatened the Church, the observance of the vernal equinox had still not been reconciled with the new calendar, which caused further disturbances. Martin Luther, for instance, thought the Church should fix Easter on a specific day, just as Christmas had been fixed as December 25 (Heilbron 39).

The papacy did not like this idea at all, as it would detract from the correct observance of this very sacred holiday. However, it did decide that the vernal equinox should be fixed in the calendar. Previously, the equinox had been set as March 25 on the Julian calendar, but by this time that day was completely incorrect in relation to the actual equinox. Fortunately, in 1568, Pope Gregory XIII decided that the entire calendar should once again be completely reworked. This time the papacy was slightly luckier, as Luigi Giglio, a doctor from southern Italy, had already made a complete plan for calendrical reformation. His idea was eventually accepted, despite lingering problems with solar cycles, as well as a pattern that would omit three leap days every four hundred years. However, this calendar was much more accurate than the pre-existing one, and thus greatly improved Church celebrations. The Gregorian calendar was widely distributed in Catholic regions by 1582.

Unfortunately, this calendar was not universally accepted, and by 1660, Britain was 355 days off the Gregorian dates (Heilbron 144). For many years, Germany also did not adopt the system because of Protestant objections that it was simply a move to prove papal domination, which similarly affected the adoption of the calendar in many other areas. Further, this new calendar had still not managed to completely eliminate the discrepancy between the date and observed day of the vernal equinox. In 1696, this became readily apparent, as the equinox occurred as far from the calendar date as was possible, which then affected date upon which the true Easter should have been celebrated. This was not a good image for the Church, as it was still struggling with the emergence Protestants, as well as its diminishing power. It needed this issue resolved quickly and definitely.

To reconcile this, a meridiana, which is a very accurate time-measuring instrument, was necessary. The Church found a man who could bring about this change in Francesco Bianchini, and an ideal site for his measuring instrument in the Church of Santa Maria degli Angeli. Bianchini was a son of science: at a young age he was given an annuity that was to be used only to buy books. He took great advantage of this, and at the age of ten, he attended the Jesuit college in Bologna. After living with and observing this Catholic order, Francesco wanted to join the Society of Jesus. However, his father overrode his wishes and sent him to the University of Padua, where he studied many subjects, specializing in mathematics (Heilbron 149). During this time, he accepted Geminiano Montanari as his mentor. Montanari had an incredible number of resources for practicing astronomy available to him, and Bianchini was afforded full use of them.

When Francesco graduated from the university, he began to pursue an ecclesiastical life. His first step was to befriend Cardinal Pietro Ottoboni, who put Bianchini in charge of his personal library, which gave him another opportunity to further his education. This patronage also helped him join Ciampini’s academy, which was a discussion group of “laymen and ecclesiastical scholars” that discussed “contemporary polite subjects” held in Ottoboni’s palace (Heilbron 150). Through this, Bianchini became acquainted with the most influential scientists of the time, including Campini, Cassini, and Leibniz.

Bianchini lucked out again when Ottoboni was named Pope Alexander VIII in 1689. The new pope showered him with gifts and positions, which he gladly accepted. The next two successors to the head of the Catholic Church, Innocent XII and Clement XI, were just as generous with their patronage. Further, Pope Clement XI was the best friend of Ottoboni, so Bianchini had even further access to the highest echelons of Catholic power. Thus, when Clement XI decreed that the calendrical problems should be absolutely resolved, Francesco was the obvious choice for the scientist to lead this latest attempt, and was given the position of secretary to the new commission of the calendar, as well as chosen to build the meridiana.

Next, the church in which the meridiana was to be placed had to be selected. A meridiana already existed in Rome, built by Kircher in the main Jesuit college, but it was not accurate enough to determine the length of the year to the second, as Cassini’s in St. Petronio was. Clement XI eventually settled on Santa Maria degli Angeli for three reasons. The first, and most obvious, was that one of its walls had an unobstructed southern view, which would allow sunlight to enter the church from the meridiana hole at any time of year. The other two reasons were more subtle. First was an architectural interest in the age of the building. Because the Baths of Diocletian were so old, their foundation had stopped settling. This would allow for maximum accuracy of the meridiana, because the sturdiness of the church itself would keep the meridiana from moving with time and thus becoming incorrect and unusable. Finally, the Baths of Diocletian were once more to be used for their historic significance. Clement XI felt that, because the Baths had earlier been used to move the calculation for when Easter was to be celebrated from the Diocletian calendar to the Dominican calendar, it was only fitting that the next improvement in the way to determine Easter would be made at the same site (Heilbron 147). And so in 1701, Bianchini began construction on the instrument that was meant to solidify the Gregorian calendar and bring about the correct celebration of Easter.

The Placement of the two Meridianae

Many meridiane had been made in churches all over Italy, as well as some in France and other European countries. The most accurate of all of these was the meridiana added to San Petronio by Giovanni Domenico Cassini, who actually replaced an existing, faulty line already installed in the church because construction was going to destroy it. Bianchini had known this meridiana master very well, and had actually built one of these lines with Cassini. When it was time to build the meridiana in Santa Maria degli Angeli, he consulted the aging scientist to reaffirm its accuracy as well as its placement. The hole for the meridiana had to be placed in the southern wall to allow the sun’s noon rays to enter the church at all times of year. This southern setting was necessary because of Italy’s northern hemispheric location. Bianchini placed the hole “20.5 meters above the ground in the south wall of an arch across the southern arm of the cross” (Heilbron 156). He chose this particular spot because it gave the longest possible line. Then the measurements for the actual placement of the line had to be made. First, it was necessary to determine where the sun’s rays would hit the floor of the church both furthest from the wall, on the winter solstice, as the sun would be lowest in the sky on that day and thus have the longest reaching ray, as well as when the light would be closest to the wall, on the summer solstice. Bianchini used an existing meridiana in the nearby Church of San Marco to check the accuracy of where he had determined that his line should be placed. He stood on the top of the Santa Maria and had one of his men signal him from San Marco when the sun hit the meridiana, and then the position of the sun’s rays on the floor of Santa Maria was marked (156). Because the location of the two churches only differed by a few arc seconds, in terms of latitude, it was a safe assumption that local noon occurred at the same time in both churches.

Bianchini was soon satisfied with the placement of his line, and began preparations for its actual construction. He used the same technique as Cassini had tried in San Petronio, as it was remarkably accurate. The first step of this method was to dig a ditch where the line was to be placed and insert a wooden canal into it, which was then filled with water to use as a level. The hole in the wall of the church was then checked to see if it was parallel to the ground, and then the diameter of this opening was made to be one-thousandth of its distance above the ground. The other aspect of these measurements was making sure that the meridiana was correctly aligned to the hole and passed directly under it. This was achieved by hanging a weighted string from the hole, and then damping its motion in water to correct for any disturbing motions. (Heilbron 90-91) The final step was then to pour metal into the canal, making sure it was of uniform height and width to maintain the maximum amount of accuracy.

Bianchini actually afforded Santa Maria degli Angeli with a second merdiana with its hole placed in the north wall, which marked the precession of Polaris, the North Star, as well as other circumpolar stars. The precession of a star is its circular path in the sky due to the rotation of the Earth, and, due to the way the starlight entered the church, the latitudes of these stars could be read off of the northern meridiana. These measurements allowed for advances in the accuracy of astronomical data, as well as increasing astronomical knowledge. Further, the time at which the light from Polaris was recorded as crossing the meridiana could be used as local midnight, which firmly established the starting of the ecclesiastical day for the Church (Heilbron 161). This was beneficial to the Catholic Church because, before this, different parts of Italy, as well as the rest of Europe, started their day at different times. This particular improvement aided in increasing the Church’s power, as they were now able to resolutely declare when the holy day began.

Precessing Star Tracks

Both the northern and the southern meridiane were rather extravagantly decorated. The hole for the southern meridiana had been surrounded by Pope Clement XI’s coat of arms, as a showing of papal power as well as a ploy by Bianchini for more papal favor. This coat of arms actually opened, and the larger hole left in the wall allowed for observation of both the sun and the moon for the times surrounding its highest ascent. Surrounding both lines, brass stars had been imbedded in the ground to mark the diurnal motions of various stars that had been observed for centuries (Heilbron 158). By each marker, the name of the star it tracks is recorded, as well as that star’s right ascension, or celestial longitude.

The Transit of the Sun across the Meridiana

By October 6, 1702, Bianchini’s meridiane was close to completion, and Pope Clement XI came to view the sun’s transit across the southern meridiana. Many others also witnessed this event, and it was noted that Bianchini had “[constructed] a line that contemporary connoisseurs rated the most beautiful, ornate, and versatile of all meridiane” (Heilbron 153). This instrument allowed Bianchini to calculate the latitude of Santa Maria degli Angeli, which he recorded as 41o54’27’’N. The real test, of course, was the length of the year as determined by two successive vernal equinoxes. Bianchini’s results ended up agreeing almost completely with the Gregorian calendar: he recorded the length of the year as 365 days, 5 hours, 49 minutes, and 1.31 seconds, as opposed to the Gregorian figure of 365 days, 5 hours, 49 minutes and 12 seconds, and the length of average lunation as almost exactly the same as the Gregorian value of 29 days, 12 hours, 44 minutes, and 3.11 seconds (his value was within one-hundredth of a second of this). And so Bianchini succeeded in proving the correctness of the Gregorian calendar, which meant that the Church could reassert its authority over when the celebration of holidays should occur, and could finally be certain of the correct observance of Easter.


Ackerman, James S. The Architecture of Michelangelo. New York: Viking Press, 1961. 123-140.

Heilbron, J. L. The Sun in the Church: Cathedrals as Solar Observatories. Cambridge: Harvard University Press, 1999.

Santa Maria degli Angeli, Rome. July 2006. Sacred Destinations: Travel Guide. 18 May 2008

Sestieri, Anna Maria Bietti, et al. Museo Nationale Romano: The Baths of Diocletian. Milan: Electa, 2002.

The Catholic Encyclopedia. 16 July 2008. New Advent. 18 May 2008