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D - 29: Did Africa push the Tower of Pisa?

Updated: Mar 26, 2021

Ever wondered why there is no big port between Genoa and Napoli when sailing down the west coast of Italy? There was one in Ostia at the time of Rome’s Imperial Hight, but it decayed a long time ago and silted up. La Spezia, the harbour built for the Royal Italian Navy got bombed out of business in 1943 by the Royal Air Force.

Usually there are harbour towns where big rivers with upstream commercial centers hit the ocean. London, Antwerp, Seville are good examples. Due to the tidal connections, they are part of the ocean world. Usually, these towns dominate their economic region. It is here where the merchants live, the people who sell the products made further upriver. As still today, those who understands clients’ needs and are closest to them, make most of the money. Money is power. Logically, the power was with London, Seville and Antwerp.

Where the Apennine mountains recede and the Arno valley opens to the east, there is surprisingly no big harbor – except tiny Livorno at the south end. Was there ever one? Of course, there was. 10km away from the shore lies Pisa with its famous Leaning Tower. A beautifully preserved medieval town surrounded by farmland. Whilst a small university and tourist town with lots of young people today, it was once big, rich and powerful. The stunning marble tower was not cheap to build. Pisa’s university had famous teachers such as Fibonacci, the mathematician. Again, not cheap – more of him in a later blog.

Love this fake photo of the Leaning Tower – the tilt was increased - but it looks cool. The alluvial ground is unevenly soft which makes the tower tilt.

When the African Plate started moving north and collided with Europe 20 million years ago, it folded the old Tethys sea floor and pushed it upwards. Italy and Dalmatia are two of these folds pushed above the waterline. The pushing was not linear and cracks between the two left large bays and indents open for the sea to fill. Africa’s push continues to today and lifts Italy by about 2 cm per year – and weather induced erosion takes it down by the same amount again. Assuming Italy is now 10 million years above water, this translates into 2’000 meters of erosion. Where did all this debris go? A quick glance at a geological map tells us:

Geological Map of Tuscany

The Quaternary greyish-blue colour indicates alluvial fillings over the last 3.6 million years. It is on these grounds that Pisa stands. These alluvial fillings are the reason why the Leaning Tower is not stable. The Arno Valley never glacierized thus the sediments never compacted. Had the Italian government not built a giant concrete platform below and stabilised the incline, the tower might well have collapsed 30 years ago. The delicate tower was built in the early 12th century and tilted over the following centuries to 5.5 degrees - the government's intervention took it back to safer 3.6. Let’s hope it stays there.

The sedimentary filling between Apennine and Central Tuscan Ridge continues to this day. Pisa is one of the oldest towns in Italy. Mentioned already in Homer’s Iliad, legend has it that the town was founded by King Nestor from Pylos, one of the participants in the War of Troy. Pisa is older than Rome and goes back to the bronze age. Recently, an Etruscan necropolis was found confirming its age. When it was found, Pisa was probably a fisher village at the shores of the Mediterranean. 1’000 years later, during the time of Emperor Augustus, the shoreline had moved 4 km west. Today, the town is at a distance of 10 km. Obviously, the town has not moved! But the shoreline did - fed by the sediments of the Arno River.

Pisa in the 5th century AD at the end of the Roman Empire – the site of the Leaning Tower is in the upper north-western corner

Pisa in the 11th century AD – a good 200 years before the peak of its power

Google Map photo of Pisa today – the old Roman town is clearly visible

Pisa was always a seafaring town – much more so than Genoa. Through the Arno valley it provided easy access to the Italian mainland and was used as naval base throughout the Roman Empire. It weathered the decline of Rome relatively well and was one of the few towns which maintained a fleet – the Byzantium Empire helped though. When twice sacked in 1004 and 1011 century by Fatimid forces, the Pisans decided to hit back. By 1015 they had removed the Muslim raiders from their base in northern Sardinia. Together with Genoa, their junior partner, the sank the Fatimid fleet in Mahdia (Tunisia) seventy years later in 1087. From now on, Pisa dominated the Western Mediterranean and was a power to reckon with. It provided shipping for the first crusade - the Popes recognized their right to govern Corsica and Sardinia.

Pisan Empire in 1090

Pisa’s power lasted for about 200 years. In 1136, it conquered Amalfi, its competitor and one of Italy's maritime republics, and established formal trade agreements with Zara, Pula, Split and Ancona in the Adriatic by 1195, interfering in Venice’s backyard. To the displeasure of its jealous neighbors, Pisa acquired vast trade concessions from the German Emperor. You need to stand in front of Pisa’s rich Duomo to understand the wealth accumulated in the 12th and 13th century. Pisa was the powerful merchant city. Its eastern upriver neighbour Florence the poor supplier of goods - how times were different!

To understand the former wealth of Pisa you need to visit Pisa's Dome and Baptistery

Fortunes changed however in 1284 in the Battle of Meloria at the mouth of the Arno river. Despite inferior numbers, the more flexible Genoese fleet sunk the Pisan ships. It was a catastrophe from which Pisa never recovered. Ships were easy to rebuild. But replacing the rowers who powered the boats was impossible. Pisa had no hinterland and could not recruit replacements. The Pisan Republic was rich enough to defend its independence against encroaching Florence for another 200 years. But the sea-based Empire was lost. By 1509 it eventually succumbed to the mighty neighbour upriver and became a province of Florence. Its hibernation which preserved the town so well for us today began.


Was Africa leaning on the Tower of Pisa? Not really. But its northward push created the preconditions for the alluvial sediments which gave Pisa its harbour and the Leaning Tower.

Our schedule does not include a stop in Pisa on the way from La Spezia to Livorno. But given this blog, we should reconsider. It is too good to miss.

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