Curious And Unusual - the floods of the river Tiber

	~ Curious And Unusual ~ - 3 - The Floods Of The River Tiber

Taking a walk through Rome's historical districts it is easy to come across a large number of old plaques, made of marble or stone, that hang from the walls of private buildings and churches. Most of them are memories of two main problems that the city had to cope with in the past. One of them is dealt with in this page, the other one is the topic of the following page. Nowadays, the course of Rome's main river is safely enclosed by huge walls, dating to the late 19th century. But in earlier times, when houses were built on the river banks, the city was likely to be flooded, sometimes rather severely. Whenever this happened, inscriptions were applied to the city's major buildings, in memory of the event, especially if the water had reached a high level. And by the large number of plaques still left, we can tell that such floods were not a rare circumstance!	a flood, in a late 1800s painting by E.Roesler Franz: the houses were submerged up to the first or even second floor, and rowing boats drifted along the streets

Taking a walk through Rome's historical districts it is easy to come across a large number of old plaques, made of marble or stone, that hang from the walls of private buildings and churches. Most of them are memories of two main problems that the city had to cope with in the past. One of them is dealt with in this page, the other one is the topic of the following page.

Nowadays, the course of Rome's main river is safely enclosed by huge walls, dating to the late 19th century. But in earlier times, when houses were built on the river banks, the city was likely to be flooded, sometimes rather severely. Whenever this happened, inscriptions were applied to the city's major buildings, in memory of the event, especially if the water had reached a high level. And by the large number of plaques still left, we can tell that such floods were not a rare circumstance!

a flood, in a late 1800s painting by E.Roesler Franz: the houses were submerged
up to the first or even second floor, and rowing boats drifted along the streets

on the western side of the church of Santo Spirito in Sassia, this plaque remembers a flood on Christmas eve of 1598: Ť ...THE TIBER GREW UP TO HERE IN THE SAME NIGHT OF OUR LORD'S BIRTH ť	Literary sources contain records of floods in Rome as early as the 5th century BC. However, during the classic age and throughout the Middle Ages the city was not flooded more than once every 50-100 years. In the 1st century AD emperor Claudius had even opened a short artificial channel by the city of Portus (still extant, now known as Fiumicino channel), in order to improve the flow of the last stretch of the Tiber.	plaque by the church of Sant'Eustachio: Ť IN YEAR 1495, THE TIBER ON A FINE DAY GREW UP TO THIS SIGN ON THE NONAE (5TH) OF DECEMBER ALEXANDER VI POPE - YEAR III ť

Then, as of the late Middle Ages, some alterations partly affecting the course of the river caused floods to become more frequent, and the damages they caused turned out more and more serious. The earliest plaque known to have been hung dated back to February 2, 1230; it could be seen on the wall of Santa Maria in Traspontina church. But when the building was taken down and rebuilt nearby, in 1564, the plaque went lost. The oldest extant specimen dates back to November 6, 1277; it can be seen under a small arch at one end of Arco dei Banchi, a narrow passage on the river side opposite Sant'Angelo Castle, connecting via del Banco di Santo Spirito and the nearby corso Vittorio Emanuele. It once hung on the opposite side of the same lane, by the old church of Santi Celso e Giuliano, until the latter was rebuilt around 1730. Another plaque in memory of the same flood hung in the aforesaid church of Santa Maria in Traspontina, but this one too went lost.	a plaque dated October 8, 1530 by the church of Santa Maria sopra Minerva: Ť UP TO HERE GREW THE TIBER AND ROME WOULD HAVE ALREADY BEEN COMPLETELY FLOODED, HAD THE VIRGIN NOT PERFORMED HERE HER SWIFT ACTION ť

Then, as of the late Middle Ages, some alterations partly affecting the course of the river caused floods to become more frequent, and the damages they caused turned out more and more serious.

The earliest plaque known to have been hung dated back to February 2, 1230; it could be seen on the wall of Santa Maria in Traspontina church. But when the building was taken down and rebuilt nearby, in 1564, the plaque went lost.
The oldest extant specimen dates back to November 6, 1277; it can be seen under a small arch at one end of Arco dei Banchi, a narrow passage on the river side opposite Sant'Angelo Castle, connecting via del Banco di Santo Spirito and the nearby corso Vittorio Emanuele. It once hung on the opposite side of the same lane, by the old church of Santi Celso e Giuliano, until the latter was rebuilt around 1730. Another plaque in memory of the same flood hung in the aforesaid church of Santa Maria in Traspontina, but this one too went lost.

a plaque dated October 8, 1530
by the church of Santa Maria sopra Minerva:
Ť UP TO HERE GREW THE TIBER
AND ROME WOULD HAVE ALREADY BEEN
COMPLETELY FLOODED, HAD THE VIRGIN
NOT PERFORMED HERE HER SWIFT ACTION ť

the oldest extant flood record (1277)
Ť UP TO HERE GREW THE TIBER
BUT, MUDDY, IT SOON RECEDED
IN THE YEAR OF THE LORD 1277,
IN THE 6TH INDICTION, ON THE 7TH DAY
OF THE MONTH OF NOVEMBER,
THE PAPAL SEE BEING VACANT ť

Resorting to old documents, etchings and other historical sources, it has been assessed that a total of 122 plaques were hung up to 1937, when Rome was flooded for the last time. Surprisingly, only few of them are no longer extant, or have been misplaced due to alterations.
A large majority of these plaques date back to the 16th-19th centuries; the older ones often feature a hand, whose finger points towards the water level reached by the flood, together with the relevant year, and sometimes a short comment.

another plaque by Santa Maria sopra Minerva's, dated November 30, 1422: Ť IN THE YEAR OF OUR LORD 1422 ON ST.ANDREW'S DAY THE TIBER'S WATER GREW TO THE TOP OF THIS PLAQUE ˇ IN THE TIME OF POPE MARTIN V ~~ 6th YEAR ~~ ť

Flood plaques can be found anywhere in the old part of the city, but there were spots that had many of them: particularly the outer wall of Sant'Angelo Castle, the river port of Ripa Grande, and the church of Santa Maria Sopra Minerva; the latter is located next to the Pantheon, on one of the lowest spots in Rome, where the water reached a higher level (see further for details).

small plaques in via Canova (left) and via dell'Arancio (right) remember
the flood of February 2, 1805, both featuring a tale-telling rowing boat
The average level (depth) of the Tiber is about 6.5 metres; the present ground level, instead, is about 9 metres taller (i.e. the approximate hight of the protective walls between which the river flows as it crosses the city). Thanks to this protection, today a flood would only occur in the case the water level reached 15 metres. But in old times, when the walls had not been built yet, 12 metres were enough to cause a flood, usually starting from the Jewish Ghetto, and sometimes the water rose even higher.
In order to keep a visual record of these event, hydrometers, i.e. graduated measures applied to a wall or to a building, came into use as of the early 1800s; however, traces of an ancient Roman one, found by Sisto Bridge, suggest that similar measures already existed in Rome's classic age.

The aforesaid church (picture below) is the only place where a small number of plaques is still visible, while due to modern alterations, they are no longer found by the other two sites, although some of them are now kept in the Museum of Sant'Angelo Castle.
Santa Maria sopra Minerva's church: flood plaques

the hydrometer by San Rocco's church	A very tall one, dated 1821, had been set by the old Ripetta river port; it consisted of several individual segments, strategically placed at different heights, so that according to the level reached by the water, the measure could be read standing on dry ground. When Ripetta port was demolished in the late 1800s, the only part of the hydrometer that was spared was the uppermost segment, which hung from an old house standing by the river bank. A few years later also this house was taken down, and the hydrometer was moved to the side of San Rocco's church, where it can be seen today. It is inscribed with the level reached by the water on the occasion of each flood (including the ones recorded in the previous centuries), the worst of which is dated 1598: over 4 metres or 12 feet above the present street level! Also the surviving column from Ripetta port is inscribed with dates of floods.	(above) column from the old Ripetta port; (below) the hydrometer by Milvio Bridge, during a recent high tide (December 2005)

When Cavour Bridge was built over the site of the old port (1896-1901) a new hydrometer replaced the preexisting one, along the flight of steps that leads to the river bank (see the illustrations).

scheme of the hydrometer by Cavour Bridge	Another one is in via dell'Arancio, facing the aforesaid bridge. Hydrometers can also be found by Milvio Bridge, and even in private buildings, such as Palazzo Corsini, in Trastevere district, and the Augustinian convent in via del Corso. Several others may have gone lost.

from the left: the hydrometer by Cavour Bridge, the one in via dell'Arancio and the one by the small Acqua Acetosa nymphaeum

the Tiber by the castle (highlighted) in A.Tempesta's map, 1593	But why were floods so frequent? Besides the absence of walls by the banks, the other main reason was the irregular width of the river bed; in particular, along its course two bottlenecks had been created. One was by Sant'Angelo Castle (left), in front of which pope Alexander VI had added a stout tower, built in the late 15th century, then removed in 1628; due to this alteration, a small embankment had been created on the western side of the river, and two arches of the bridge had been obstructed. Here the water also turned particularly turbulent due to the river's double bend, but Sant'Angelo Bridge, whose main structure is still basically the original one (2nd century AD), was perfectly built, and never collapsed. The other spot was by Villa Farnesina (right), the large mansion of the Farnese family located in Trastevere district, whose gardens, in time, had been enlarged by reducing the river's width.	Villa Farnesina (highlighted) in Giambattista Nolli's map, 1748

At the beginning of the rainy season, i.e. in October, the underground aquifers, partly dry after the summertime, were saturated again; only after this had happened, any further increase of the Tiber's flow due to rainfalls would mainly affect its level, giving reason for a higher frequency of floods from late November to mid winter, as testified by the dates on most plaques. When the water reached the streets, it followed the ground features, sloping towards the districts whose ground level was low. Furthermore, the water could also follow the Cloaca Maxima, the ancient Roman sewage whose net of tunnels still runs underground, usually flooding Pantheon Square, one of the lowest spots in Rome, and then spreading to the surrounding district.	the outlet of the Cloaca Maxima by the Tiber bank

At the beginning of the rainy season, i.e. in October, the underground aquifers, partly dry after the summertime, were saturated again; only after this had happened, any further increase of the Tiber's flow due to rainfalls would mainly affect its level, giving reason for a higher frequency of floods from late November to mid winter, as testified by the dates on most plaques. When the water reached the streets, it followed the ground features, sloping towards the districts whose ground level was low. Furthermore, the water could also follow the Cloaca Maxima, the ancient Roman sewage whose net of tunnels still runs underground, usually flooding Pantheon Square, one of the lowest spots in Rome, and then spreading to the surrounding district.

the outlet of the Cloaca Maxima by the Tiber bank

plaque remembering Rome's last flood (December 17, 1937) by the church of San Bartolomeo, on the Tiber Island	Sometimes large parts of the city were reached by the flood, particularly the plains of the ancient Campus Martis area (i.e. once the western part of ancient Rome, now the historical centre), and the valleys between the city's many hills, as seen in the map below. There were districts, such as the Jewish ghetto, where the water could reach up to the houses' third floor.

On top of this, during a flood the several small floating mills that once were moored along the river often broke loose, and drifted until they reached the closest bridge: here they obstructed its arches, either partly or completely, thus worsening the overflow and the pressure exerted by the water against the bridge itself. Today the risk of a flood is very unlikely, thanks to the walls, about 12 m or 39 ft tall, that protect the city on both sides of the Tiber. After the last serious overflow, in 1870 (many relevant plaques exist), the decision of building them was taken, and their making started in 1875. Since then, Rome was flooded again only three times, the last one in 1937 (picture on the right). photograph taken in via Portuense, in December 1937 →

On top of this, during a flood the several small floating mills that once were moored along the river often broke loose, and drifted until they reached the closest bridge: here they obstructed its arches, either partly or completely, thus worsening the overflow and the pressure exerted by the water against the bridge itself.

Today the risk of a flood is very unlikely, thanks to the walls, about 12 m or 39 ft tall, that protect the city on both sides of the Tiber. After the last serious overflow, in 1870 (many relevant plaques exist), the decision of building them was taken, and their making started in 1875. Since then, Rome was flooded again only three times, the last one in 1937 (picture on the right).

photograph taken in via Portuense, in December 1937 →

	the course of the Tiber and the city's land features: HILLS 1 ˇ Capitolium 2 ˇ Palatine 3 ˇ Quirinal 4 ˇ Viminal 5a 5b 5c ˇ Esquiline 6 ˇ Coelian 7a 7b ˇ Aventine 8 ˇ Janiculum 9 ˇ Vatican AREAS AND BUILDINGS A ˇ Colosseum B ˇ Roman Forum C ˇ Campus Martis D ˇ Pantheon E ˇ Tomb of Octavianus Augustus F ˇ Sant'Angelo Castle G ˇ St.Peter's and the Vatican

However, the price payed for this security measure was the loss of several old houses by the river banks and of the two ports (Ripa Grande and Ripetta), plus some alterations suffered by ancient bridges, such as Cestius Bridge (I century BC, see also The Tiber Island in this section): many typical views were forever lost, as the following comparison clearly shows.

a view of the river from Ripetta port in the late 1800s (painting by E.Roesler Franz), and the same spot today

the arches of Sant'Angelo Bridge obstructed by boats adrift, during the high water in December 2008	Nevertheless, the danger has been minimized, but not completely overcome: particularly rainy seasons, possibly combined with accidents similar to the ones previously described, due to the large boats moored by the banks (picture on the left), might still cause damages to bridges and make the water level exceed the height of the walls.