Practical Engineering
Published 21 Oct 2025All the things I love about Niagara Falls
The same thing that makes Niagara Falls impressive for tourists (the big drop) makes it valuable for power and a major challenge for shipping. And out of that comes all kinds of fascinating infrastructure.
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!
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February 26, 2026
The Hidden Engineering of Niagara Falls
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February 10, 2026
QotD: The (historical) walls of Jericho
These strategic (and operational) considerations dictate some of the tactical realities of most sieges. The attacker’s army is generally going to be larger and stronger, typically a lot larger and stronger, because if the two sides were anywhere near parity with each other the defender would risk a battle rather than submit to a siege. Thus the main problem the attacker faces is access: if the attacker can get into the settlement, that will typically be sufficient to ensure victory.
The problem standing between that attacking army and access was, of course, walls (though as we will see, walls rarely stand alone as part of a defensive system). Even very early Neolithic settlements often show concerns for defense and signs of fortification. The oldest set of city walls belong to one of the oldest excavated cities (which should tell us how short the interval between the development of large population centers and the need to fortify those population centers was), Jericho in the West Bank. The site was inhabited beginning around 10,000 BC and the initial phase of construction on what appears to be a city wall reinforced with a defensive tower was c. 8000 BC. It is striking just how substantial the fortifications are, given how early they were constructed: initially the wall was a 3.6m stone perimeter wall, supported by a 8.5m tall tower, all in stone. That setup was eventually reinforced with a defensive ditch dug 2.7m deep and 8.2m wide cutting through the bedrock (that is a ditch even Roel Konijnendijk could be proud of!), by which point the main wall was enhanced to be some 1.5-2m thick and anywhere from 3.7-5.2m high. That is a serious wall and unlikely the first defensive system protecting the site; chances are there were older fortifications, perhaps in perishable materials, which do not survive. Simply put, no one starts by building a 4m by 2m stone wall reinforced by a massive stone tower and a huge ditch through the bedrock; clearly city walls [were] something people had already been thinking about for some time.
I want to stress just how deep into the past a site like Jericho is. At 8000 BC, Jericho’s wall and tower pre-date the earliest writing anywhere (the Kish tablet, c. 3200 BC) by c. 4,800 years. The tower of Jericho was more ancient to the Great Pyramid of Giza (c. 2600 BC), than the Great Pyramid is to us. In short, the problem of walled cities – and taking walled cities – was a very old problem, one which predated writing by thousands of years. By the time the arrival of writing allows us to see even a little more clearly, Egypt, Mesopotamia and the Levant are already filled with walled cities, often with stunningly impressive stone or brick walls. Gilgamesh (r. 2900-2700 BC) brags about the walls of Uruk in the Epic of Gilgamesh (composed c. 2100) as enclosing more than three square miles and being made of superior baked bricks (rather than inferior mudbrick); there is evidence to suggest, by the by, that the historical Gilgamesh (or Bilgames) did build Uruk’s walls and that they would have lived up to the poem’s billing. Meanwhile, in Egypt, we have artwork like the Towns Palette, which appears to commemorate the successful sieges of a number of walled towns
So a would-be agrarian conqueror in Egypt, Mesopotamia or the Levant, from well before the Bronze Age would have already had to contest with the problem of how to seize fortified towns. Of course depictions like these make it difficult to reconstruct siege tactics (the animals on the Towns Palette likely represent armies, rather than a strategy of “use a giant bird as a siege weapon”), so we’re going to jump ahead to the (Neo)Assyrian Empire (911-609 BC; note that we are jumping ahead thousands of years).
Bret Devereaux, “Collections: Fortification, Part I: The Besieger’s Playbook”, A Collection of Unmitigated Pedantry, 2021-10-29.
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January 2, 2026
How did Ancient Romans build their roads?
Metatron
Published 2 Sept 2025Roman road construction was a marvel of ancient engineering that began in earnest around 312 BC with the famous Appian Way. The Romans developed a systematic approach that would serve their empire for centuries, creating over 250,000 miles of roads by 200 AD.
Their construction process started with careful surveying using tools called groma and chorobates to ensure straight lines and proper gradients. Roman engineers would then excavate a roadbed typically 14 to 16 feet wide, digging down 3 to 5 feet deep depending on local conditions and expected traffic. The foundation layer, called the statumen, consisted of large flat stones carefully fitted together. Above this came the rudus, a layer of crushed stone and mortar about 9 inches thick, followed by the nucleus, a finer mixture of gravel and mortar. The top surface, known as the summum dorsum, was made of large polygonal stone blocks called silex, fitted so precisely that no mortar was needed between them. These roads were built with a slight crown in the center to promote drainage, and ditches were dug alongside to carry away rainwater.
Roman construction crews, often composed of soldiers, would work in organized teams with specialized roles for quarrying stone, mixing mortar, laying foundations, and fitting the surface blocks. The entire process could take months or even years for major routes, but the result was a road surface so durable that many Roman roads remained in use well into the medieval period and beyond. Quality control was maintained through strict military discipline and the personal responsibility of engineers who literally put their names on milestone markers. By 117 AD, at the height of the empire, this road network connected Britain to the Middle East and North Africa to the Rhine frontier, facilitating trade, communication, and military movement across the known world.
#romanempire #ancientrome #romanroads
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March 20, 2025
Everyday Life in the Roman Empire – Demography, Income, Life Expectancy
seangabb
Published 12 Sept 2024Part seven in a series on Everyday Life in the Roman Empire, this lecture discusses demography and life chances during the Imperial period. Here is what it covers:
Introduction – 00:00:00
Our Statistical Civilisation – 00:00:24
Ancient “Statistics” – 00:08:05
How Many Roman Citizens? – 00:18:04
Population of the Empire – 00:21:36
City Populations – 00:27:45
Average Incomes – 00:36:27
Life Expectancy – 00:35:37
Country Life – 00:52:06
Population of Rome – 00:54:39
Feeding Rome – 00:57:40
Roman Water Supply – 01:00:44
Bathing and Sanitation – 01:04:16
Hygienic Value – 01:04:16
Bibliography – 01:06:17
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January 18, 2025
Is the World Really Running Out of Sand?
Practical Engineering
Published 1 Oct 2024Sand: a treatise …
There’s a lot changing in the construction industry, and a lot of growth in the need for materials like sand and gravel. But I don’t think it’s fair to say the world is running out of those materials. We’re just more aware of all the costs involved in procuring them, and hopefully taking more account for how they affect our future and the environment.
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December 9, 2024
QotD: The downfall of Boeing
There’s a lot to love about an engineer-dominated corporate culture. For starters, it has a tendency to overengineer things, and when those things are metal coffins with hundreds of thousands of interacting components, filled with people and screaming through the air at hundreds of miles an hour, maybe overengineering isn’t so bad. These cultures also tend to be pretty innovative, and sure enough Boeing invented the modern jet airliner and then revolutionized it several times.
But there are also downsides. As any Googler will tell you, these companies usually have a lot of fat to trim. Some of what looks like economic inefficiency is actually vital seed corn for the innovations of the future, but some of it is also just inefficiency, because nobody looks at the books, because it isn’t that kind of company. Likewise, being highly deliberative about everything can lead to some really smart decision making and avoidance of group think, but it can also be a cover for laziness or for an odium theologicum that ensures nothing ever gets done. Smart managers steeped in this sort of culture can usually do a decent job of sorting the good from the bad, but only if they can last, because you see there’s a third problem, which is that almost everybody involved is a quokka.
Engineers, being a subspecies of nerds, are bad at politics. In 1996, Boeing did something very stupid and acquired a company that was good at politics. McDonnell Douglas, another airplane maker, wasn’t the best at making airplanes, but was very good at lobbying congress and at impressing Wall Street analysts. Boeing took over the company, but pretty much everybody agrees that when the dust had settled it was actually McDonnell Douglas that had taken over Boeing. One senior Boeing leader lamented that the McDonnell Douglas executives were like “hunter killer assassins”. No, sorry bro, I don’t think they were actually that scary, you were just a quokka.
Anyway, the hunter killer assassins ran amok: purging rivals, selling off assets, pushing through stock buybacks, and outsourcing or subcontracting everything that wasn’t nailed down. They had a fanaticism for capital efficiency that rose to the level of a monomania,1 which maybe wasn’t the best fit for an airplane manufacturer. And slowly but surely, everything went off the rails. Innovation stopped, the culture withered, and eventually planes started falling out of the sky. And now the big question, the question Robison just can’t figure out. Why?
John Psmith, “REVIEW: Flying Blind by Peter Robison”, Mr. and Mrs. Psmith’s Bookshelf, 2023-02-06.
1. This is how you know this story took place in an era of high interest rates!
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November 17, 2024
Three (more) Forgotten Roman Megaprojects
toldinstone
Published Jul 19, 2024This video explores another three forgotten Roman megaprojects: the colossal gold mines at Las Médulas, Spain; the Anastasian Wall, Constantinople’s outer defense; and Rome’s artificial harbor at Portus.
Chapters:
0:00 Las Médulas
3:13 The Anastasian Wall
5:24 Portus
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November 14, 2024
Following the Longest Roman Aqueduct
Scenic Routes to the Past
Published Jul 19, 2024Tunisia’s Zaghouan Aqueduct, built to serve Carthage in the second century, is among the longest and most impressive of all Roman aqueducts. This video follows the aqueduct from the monumental fountain at its source to the grandiose baths at its terminus.
Historic tours with toldinstone: https://toldinstone.com/trips/
Check out my other channels, @toldinstone and @toldinstonefootnotes
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September 29, 2024
This Bridge Should Have Been Closed Years Before It Collapsed
Practical Engineering
Published Jun 18, 2024Why Fern Hollow Bridge collapsed.
This is a crazy case study of how common sense can fall through the cracks of strained budgets and rigid oversight from federal, state, and city staff. And the lessons that came out of it aren’t just relevant to people who work on bridges. It’s a story of how numerous small mistakes by individuals can collectively lead to a tragedy.
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May 31, 2024
How To Install a Pipeline Under a Railroad
Practical Engineering
Published Feb 20, 2024I’m on location to document the installation of a water transmission line below two railroad tracks.
Huge thanks to our project partners!
Owner: Crystal Clear Special Utility District
General Contractor: ACP
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May 26, 2024
Evolution of The Churchill Tank | “No Damn Good”?
The Tank Museum
Published Feb 17, 2024Designed by a company that had never built a tank before with the Prime Minister, Winston Churchill, looking over their shoulders and plagued by mechanical teething troubles, the Churchill tank had unpromising beginnings. Despite this, it became one of the most successful British tanks of WW II: heavily armoured, not fast but with superb climbing ability, the Churchill served not only as a gun tank but the basis many of the specialised vehicles that helped the British and Canadian Armies ashore on D-Day.
00:00 | Intro
01:20 | History – What was needed?
03:38 | Design, Weaponry and Armour
08:44 | Up-gunned and Upgraded
13:59 | A Look Inside
17:51 | Combat Performance
20:23 | Multi-use Platform
23:10 | ConclusionThis video features archive footage courtesy of British Pathé.
#tankmuseum
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April 21, 2024
How The Channel Tunnel Works
Practical Engineering
Published Jan 16, 2024Let’s dive into the engineering and construction of the Channel Tunnel on its 30th anniversary.
It is a challenging endeavor to put any tunnel below the sea, and this monumental project faced some monumental hurdles. From complex cretaceous geology, to managing air pressure, water pressure, and even financial pressure, there are so many technical details I think are so interesting about this project.
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April 1, 2024
How Railroad Crossings Work
Practical Engineering
Published Jan 2, 2024How do they know when a train is on the way?
Despite the hazard they pose, trains have to coexist with our other forms of transportation. Next time you pull up to a crossbuck, take a moment to appreciate the sometimes simple, sometimes high-tech, but always quite reliable ways that grade crossings keep us safe.
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March 23, 2024
The Roman Army’s Biggest Building Projects
toldinstone
Published Dec 15, 2023The greatest achievements of the Roman military engineers.
Chapters:
0:00 Introduction
0:38 Marching camps
1:36 Bridges
2:40 Siegeworks
3:26 PIA VPN
4:32 Permanent forts
5:49 Roads
6:24 Frontier defenses
7:41 Canals
8:21 Civilian projects
8:54 The aqueduct of Saldae
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March 11, 2024
Why Railroads Don’t Need Expansion Joints
Practical Engineering
Published Dec 5, 2023A friendly overview of thermal effects on railways.
Errata: At 9:00, the left column of calculations is incorrectly labeled “SI.” It should be imperial. Whoops!
Just as all materials have a mostly linear relationship between temperature change and length change, all materials also have a similar relationship between stress and change in length (often called strain). And this is part of the secret to continuous welded rail: restrained thermal expansion. You can overcome one with the other.
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