How Engineers Straightened the Leaning Tower of Pisa

One of my favorite civil engineering projects!

The lean isn’t just a fascinating oddity; it is integral to the historical character of the tower. It’s a big part of why we care. Unlike the millions of photos of tourists pretending to hold the Pisa tower up, the contractors, restoration experts, and engineers actually did it (for the next few centuries, at least).

Sources: The script is primarily based on the papers linked below.

Practical Engineering is a YouTube channel about infrastructure and the human-made world around us. It is hosted, written, and produced by Grady Hillhouse. We have new videos posted regularly, so please subscribe for updates. If you enjoyed the video, hit that ‘like’ button, give us a comment, or watch another of our videos!

CONNECT WITH ME
____________________________________

SPONSORSHIP INQUIRIES
____________________________________

DISCLAIMER
____________________________________
This is not engineering advice. Everything here is for informational and entertainment purposes only. Contact an engineer licensed to practice in your area if you need professional advice or services. All non-licensed clips used for fair use commentary, criticism, and educational purposes.

SPECIAL THANKS
____________________________________
This video is sponsored by Nebula.
Stock video and imagery provided by Getty Images, Shutterstock, and Videoblocks.
Tonic and Energy by Elexive is licensed under a Creative Commons Attribution License
Video by Grady Hillhouse
Edited by Wesley Crump
Produced by Ralph Crewe
Graphics by Nebula Studios

[mfaizsyahmi]

I find it very amusing that the sidewalks are actually load bearing, not just for pedestrians but the entire tower.

[certiPHIer]

I was there in 1987, 3 years before the tower was closed for repairs. It is a terribly disorienting building to climb the stairs to the top, not only because of the lean that causes you to (correctly) feel like you are leaning in every direction in sequence, like someone terribly drunk, but also because the centuries of foot traffic on the steps have caused them to wear out unevenly, so they are dished out where the feet have trafficked the most. Plus the single narrow spiral stair has both people climbing up and people climbing down at the same time. It was also ver scary when you got to the top, because from the lowest side of the platform, you could not see the base of the tower beneath you, the lean was so great. But I'm glad I had the opportunity and really glad it did not collapse while I was in the tower. I'm so happy it has been stabilized now and future generations will have a chance to experience it themselves.

[DrRadula]

There's just something extremely joyful about a guy being able to say "recreational geology" with a straight face and a genuine smile

[chrissistrunk]

I love the nod to Mitch Hedberg at the beginning. "A river used to run into the Ligurian Sea, It still does...but it did back then too"

[kenchilton]

A couple other ideas that were rejected were installing a tube system under the foundation to freeze the water in the subsoil, controlling the temperature according to the lean, or using hydraulically injected foam to correct the lean in conjunction with injecting a water-cured polymer to harden the subsoil.

[maxcactus]

5:23 - 5:48 Sneaky, sneaky Grady!!! The Tower was increasinig in it's tilt that entire 25 seconds and I only noticed the difference when I did a quick rewind of the 20 seconds prior to 5:48 to show the stark difference once the catino was removed. Very subtle and VERY well done in your graphics - bravo!! And overall, this video was beautiful and a wonderful illustration of the tremendous, positive real world impact engineer's have on the world!!

[RocLobo]

It's absolutely wonderful that the engineers locked the leaning side into the sidewalk to support it. Medieval architects were something else.

[beardysam]

Fun fact: The engineers from Imperial College London that assisted this project had already stabilised the Queens Tower at their university in London, and later stabilised Big Ben with the same methods.

[rhouser]

“If you’re into recreational geology & heavy construction!” 😂 I really wasn’t until I started watching your channel! Now I think about it driving down the road looking at anything that was built.

[danielbarreiro]

I saw the bracing of the tower when visiting Italy in the late 90s, however, I didn't get to see the actual fix being done at ground level since the work area was boarded all around. The cables clearly looked temporary, as they were not fixed permanently to the tower rather they embraced the exterior with wood planks to shield the stone from the cable. For everything I saw above the edge of the fence, I guessed they were pumping some sort of cement mix under it, not taking out soil. They did a nice trick there. Thanks for telling the story.

[MinneapolisRaven]

Grady, your channel is my favorite example of why YouTube channels are so much better than regular TV.
So many old cable shows would breeze over topics and say "amazing, right?"
Those shows were dumbed down and insulting; while your videos are deeply interesting and, by inspiring young people to pursue an engineering career, literally making the world a better place. Thank You!

[TheRealPOTUSDavidByrd]

The ending monologue about the team working to continue an 800 year old project was oddly touching. Kudos!

[magimix]

The tower is *curved*?! That is amazing. I can't believe I never knew that.

[Harborman]

Back in the early 80s I lived in Egypt and met some Italian engineers that lived in the same hotel that I was staying. I told them what I would do to fix the tower and this is exactly what I told them to do. Two years ago the History channel showed what they did. That really made my day.

[TheLastTater]

I just visited the leaning tower of Pisa a month ago on my honeymoon and it’s amazing thing to see in person. I learned all about its lean and foundation changes. So awesome you made a video on it! I loved it

[georgiabelle]

I saw the title and thought, “What? Again?” I’m glad I didn’t miss anything as big as a second stabilization, and I’m happy to finally hear the story of how it was done.

[kenbrown]

I'm reminded of the stories a friend of mine tells. he worked construction on housing developments in Florida, and in many places, the slab foundations for houses floated on wet sand until the house was built and slowly compacted the water out. if the house was built asymmetrically, the foundation would tilt under the unbalanced load, so they had to be careful how they loaded the material onto the slab.

[joesomebody]

Awesome story, great use of diagrams and models to visually show what you are explaining.
Thanks for making and sharing this video.

[tomypreach]

I've had many teachers throughout my life. This channel continues to be on the top ten list of most influential.

[MajoraZ]

Another video like this you could do on a many-centuries-long engineering project, albeit one that ended in failure, could be the Aztec capital/Mexico City's water and soil issues: Tenochtitlan was a giant city with Venice-like canals built on both a natural island and expanded with a grid of artificial islands over time, with a complex series of levees, aqueducts, and other systems to intake fresh water and to avoid flooding. When the city was sieged by Conquistadors and armies from other local city-states, much of that infrastructure was destroyed and Mexico City, built on the ruins, had regular issues with flooding. Eventually in the 1700s intensive draining efforts to drain the series of 5 lakes in the valley got underway (after previous management attempts) and continued to the 20th century, which backfired as it ended up almost entirely depleting the aquafer and led to the liquefaction and compaction of the loose lakebed sediment, especially as Mexico City's urban sprawl has spread over much of the former lakebed and added (millions) of tons of weight.

As a result, today, Mexico City is sinking... rapidly. Some parts of the city as fast as 50 centimeters/20 inches a year, and it's not predicted to stop for many decades, and recent reports have found that it's past the point of no return already. There's constant issues with sewage lines, subways, etc breaking as a result of this, and it's renewing flooding issues while the lakes are mostly gone (save some surviving Aztec period canal systems in Xochimilco, which too are threatened by this), now it's worsening issues with retaining rainwater.

Some other channels have covered this already, but I find many of the videos don't delve into the specific engineering details or all the historical context: We know the specifics of how many of the Aztec aqueducts worked (the main aqueduct which sourced water from Chapultepec for example had dual ceramic pipes with a switching mechanism) and with the specific drainage projects, yet neither has really been covered with detailed diagrams and like yet like you did here. I also find people only mention Tenochtitlan, sometimes even mistakenly showing the valley being empty aside from Teno. with it only urbanizing as Mexico City grew, despite there being hundreds of other Aztec cities in the Valley some of which had their own lake infrastructure/engineering efforts (like Texcoco's Texcotzingo waterworks system) some of which played a role in these events; and there being significant urbanization there for thousands of years before the Aztec period, like with Tlatilco, Cuicuilco, Teotihuacan, etc.

So I think there's still room for you or the Wendover team you mentioned you work with to contribute to the topic in a way other people haven't done so yet. I actually work with history and archeology channels with researching and fact checking their Mesoamerican stuff and would be down to help out if you ever wanted to cover it!