PE of Crabtree Group Civil Engineers and Town Planners. CNU Rainwater www.cnu.org. Rainwater-in-Context at Google Groups. TransectCodesCouncil www.transect.org
on the urban armature
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Paul Crabtree retweeted
Modern concrete starts falling apart in a few decades. Roman concrete has been sitting in seawater for 2,000 years and getting stronger.
The Romans figured out that volcanic ash changed everything. They dug it from around the Bay of Naples, near the town of Pozzuoli, mixed it with lime and chunks of rock, and got a material that could set even underwater. The architect Vitruvius wrote about it in the first century BC. Pliny the Elder claimed that once it hit the sea, it became a single mass of stone the waves couldn't break.
He wasn't exaggerating. Roman harbor walls and piers built in the sea are still standing today, while modern concrete in the same conditions cracks and crumbles.
For a long time nobody knew why. In 2017, a geologist named Marie Jackson studied samples from ancient Roman piers and found the answer. Seawater soaking into the concrete was reacting with the volcanic ash and growing rare mineral crystals inside it. The ocean that destroys our concrete was actually reinforcing theirs.
Then in 2023, MIT researchers found something else. Roman concrete is full of little white chunks of lime that scholars had long assumed were just sloppy mixing. They weren't. The Romans were likely mixing with hot quicklime, and those chunks acted as a built-in repair kit. When a crack formed and water seeped in, the lime dissolved and filled the crack back in. Self-healing concrete, two thousand years before anyone used that phrase.
The Romans built on a scale that shows they trusted it completely. Herod the Great had volcanic ash shipped all the way from Italy to build an artificial harbor at Caesarea in Judea. Hadrian's Pantheon in Rome, finished around 125 AD, still has the largest unreinforced concrete dome on earth, about 142 feet across. No steel. Nothing holding it up but the concrete itself.
After the Western Empire collapsed, the know-how faded. Medieval Europe mostly built in stone and timber. Modern Portland cement wasn't patented until 1824, and it still can't match what the Romans were pouring into the sea before the birth of Christ.
Paul Crabtree retweeted
Most people in ancient Rome lived in rented apartments.
Today, a 1,900-YEAR-OLD Roman apartment block is still standing in Rome, at the foot of the Capitoline Hill.
Records from the 4th century say the city had about 46,000 apartment blocks, called “insulae.” In comparison, there were fewer than 2,000 private houses.
Some of these buildings were so tall that Augustus banned anything higher than 70 Roman feet (about 20 meters). Later, Emperor Trajan lowered the limit to 60 Roman feet.
The floors worked the opposite way from today. Shops were on the ground floor, and rich tenants lived on the first floor. The higher you went, the cheaper the rent and the worse the living conditions: there was no running water, there were fewer windows, and there were a lot of stairs to climb.
Paul Crabtree retweeted
Build as if you only had a wheelbarrow, and you’ll preserve much more of the character of the land and streams, and also many of the trees. Your lots will be more valuable and far less boring in the early years than land scraped flat as per standard engineering practice.
Paul Crabtree retweeted
The Hoover Dam was built in 4 years and 2 months (1931–1935).
It contains 2.48 million cubic metres of concrete. Enough to build a 2-lane highway from New York to San Francisco and back.
At peak, 5,200 workers were on site simultaneously. 113 died during construction.
It generates 4 billion kWh per year, enough to power 1.3 million US homes.
At completion, it was the world's largest hydroelectric power station and the world's largest concrete structure.
Both records have since been broken.
But the dam still runs on its original turbines, 90 years later.
Paul Crabtree retweeted
In the 1950s, flying cars were the ultimate symbol of the future.
It’s 2026.
They’re here.
The future has arrived. ✈️
Paul Crabtree retweeted
'The definition of insanity is doing the same thing over and over again and expecting a different result.'
— Rita Mae Brown
Case #1237 of using traffic engineering to solve the problems of traffic engineering.
📍 #Alexandria, Egypt 🇪🇬.
Paul Crabtree retweeted
In Centuripe, the landscape determined the streets, and the streets gave the town its extraordinary shape.
The town you see today largely dates from the 16th century, but Centuripe’s story reaches back to a Sicel settlement founded in the 8th century BC and a prosperous Roman city.
Paul Crabtree retweeted
“Streets, the main public places of a city, are its most vital organs.” - Jacobs
“If you want to know what a culture values, look at what it builds. Our cities and towns are some of the greatest works of human civilization. They all began with their streets.” - Dover+Massengale
ALT A paperback book, “Street Design: The Secret to Great Cities and Towns” sits in the middle of a brick paved and tree lined street in Delft, The Netherlands.
That’s 18 miles per hour. Come on USA, we can do this! #20isPlenty
Resultados bajada límites de velocidad a 30 km/h en ciudades europeas:
▫️-23% colisiones y atropellos
▫️-37% fallecidos
▫️-18% emisiones
▫️-2,5 dB ruido
▫️-7% consumo combustible xitter.cf/davidlois_uned/status/…
Transitions from 8 car lanes to 4! Remarkable - can’t wait to visit again.
Els nous Champs Elysées de Paris, ja en construcció
Totes les grans ciutat ho tenen clar #PrimerElsVianants🚶♀️🚶🚶♂️
Paul Crabtree retweeted
Rest in Peace, Wendell Berry. You brought light and life and made the world a better place. My sincerest thanks to you.
Do not live for death,
pay it no fear or wonder.
This is the firmest law
of the truest faith. Death
is the dew that wets the grass
in the early morning dark.
It is God’s entirely. Withdraw
your fatal homage, and live.
War is only a distraction.
Full music video of The Sinners is on YouTube now! Let me know what parts hit home the most for you. Below to watch 👇🤍
youtu.be/anrRWbb1iZM?si=L6_R…
Paul Crabtree retweeted
Roman roads were built to last.
Not for decades. For millennia.
The construction sequence, documented by Vitruvius and confirmed by modern excavations, was:
1. STATUMEN: large flat stones laid directly on compacted subgrade
2. RUDUS: a layer of smaller stones or rubble, set in lime mortar, 20–30 cm thick
3. NUCLEUS: concrete made from lime, coarse sand, and gravel, 15 cm thick
4. SUMMUM DORSUM: the surface layer, flat polygonal stones fitted together without mortar, slightly crowned at the centre to drain water
The total depth: up to 1.5 metres in some roads.
The road was cambered, raised at the centre, so rainwater drained to drainage ditches on each side.
The drainage ditches were themselves engineered: lined with stones, at calculated gradients.
Roman roads didn't fail because of moisture. Most ancient roads do.
By 200 AD, the Roman road network spanned approximately 400,000 km.
Over 80,000 km were stone-paved.
In Britain, several modern roads run directly above Roman foundations.
The A2 from London to Dover follows the line of Watling Street.
The M1 motorway in Hertfordshire runs parallel to the Roman road it replaced.
The roads worked because the engineers understood the problem was not the surface.
It was water management beneath the surface.
That's still true of every road built today.
Paul Crabtree retweeted
The coolest technology in a heatwave? Trees.
Every tree planted today helps create a cooler, greener and healthier London tomorrow.
We've already planted more than 640,000 trees since 2016, and we're continuing to grow and protect our urban forest to help London adapt to hotter summers.
And … Great engineers design to improve the human experience of civilization.
The difference between good and great engineers is not technical ability.
It's these six things:
1. THEY DEFINE THE PROBLEM BEFORE SOLVING IT
Good engineers solve the problem they're given.
Great engineers ask whether it's the right problem.
The best solution to the wrong problem is still the wrong solution.
2. THEY COMMUNICATE UP, DOWN, AND SIDEWAYS
Technical excellence that can't be communicated doesn't scale.
Great engineers write clearly, speak plainly, and translate between technical and non-technical fluently.
This skill multiplies their impact by 10x.
3. THEY OWN FAILURES WITHOUT EXCUSE
Good engineers explain why something failed.
Great engineers explain what they will do differently.
Accountability without defensiveness is rare. It's also what builds trust.
4. THEY KNOW WHAT THEY DON'T KNOW
Good engineers are confident in their domain.
Great engineers are explicit about the boundaries of that domain.
"I don't know – but I know who does" is one of the most valuable sentences in engineering.
5. THEY THINK IN SYSTEMS, NOT COMPONENTS
Every component has a context.
Great engineers design for the context, not just the component.
The part that works perfectly in isolation and fails in the system is the most common engineering story.
6. THEY MAKE DECISIONS WITH INCOMPLETE INFORMATION
The real world never has all the data.
Great engineers develop judgement – the ability to make good decisions when the information is ambiguous, the timeline is short, and the stakes are real.
Technical skill gets you to good.
These six things get you to great.
Spartans! Bad ass military… but what else?
Sparta had one job. Produce the best soldiers who ever lived. Everything else in daily life bent around that single goal, and it was brutal.
It started at birth. According to the ancient accounts, a newborn was brought before a council of elders who decided if it looked strong enough to be worth raising. This part is debated by historians, but the Spartans themselves believed weakness could not be tolerated.
At age 7, boys were taken from their mothers. Just taken, and moved into state barracks to begin the agoge, the most famous training system in history. From then on the state raised you, not your family.
They were kept cold, barefoot and hungry on purpose. Their beds were reeds they had to rip from the riverbank with their bare hands. They were deliberately underfed, and here is the twist. They were expected to steal extra food to survive. But if you got caught stealing, you were beaten savagely. Not for stealing. For being clumsy enough to get caught.
The food was legendary for being awful. The famous dish was a black broth made of pork, blood, salt and vinegar. A visitor from another city tried it once and said he finally understood why Spartans did not fear death.
They trained boys to speak in short, cutting one liners. We still call it laconic today, from Laconia, the region around Sparta. When an enemy king warned them "If I invade, I will raze your city to the ground," the Spartans sent back a single word reply. "If."
Grown men did not really live at home either. Even married men ate every night at a communal mess hall with their unit, sharing the same rough food, because your loyalty was supposed to be to your brothers in arms first and your household second. Young husbands actually had to sneak out to visit their own wives.
Money was designed to be useless. Instead of gold and silver, Spartans used heavy iron bars so bulky you needed a cart to move any real amount. The whole point was to make wealth and bribery pointless, so no one could get rich or soft.
And the strangest part to outsiders. Spartan women were the freest in all of Greece. While other Greek women were shut indoors, Spartan girls were fed well, educated, and made to run, wrestle and throw the javelin, because Spartans believed strong mothers produced strong sons. Women could own property, and eventually owned a huge share of Spartan land. They were famous for speaking their minds to men, which shocked the rest of Greece.
But the whole system sat on a dark foundation. The Spartans were vastly outnumbered by the helots, a population of enslaved people who did all the farming so that citizens could train for war full time and never work. To keep them terrified and controlled, Sparta every year formally declared war on its own helots, so that killing one was never a crime. Young Spartans were even sent out in secret death squads to hunt and kill the strongest helots as a rite of passage.
So daily life in Sparta was not really living in the way we mean it. It was one long, cold, hungry preparation for battle, held up by fear on every side. It built the most feared army in the ancient world, and almost nothing else. They wrote no philosophy, built no great temples, left no art. When Sparta finally fell, it left behind no ruins worth the name, just the story.
Which is why a historian joked that if you judged the two cities only by their remains, no one would ever believe Sparta had been half as powerful as the legends say.
