How did bridge builders of old ensure both ends of the bridge would perfect meet in the middle before laser measuring was around?
In: Engineering
Modern measuring tools are more practical and resistant to human error, but precision isn’t necessarily a modern thing. The [theodolite](https://en.m.wikipedia.org/wiki/Theodolite) has been around since 1600 and along with other precise distance measuring tools it allowed for incredible precision in building.
Antique topography instruments were much more mechanical and human dependent, but topography isn’t a new science and the old instruments weren’t necessarily much less precise than modern instruments.
Today we seem puzzled that people could have built anything without digital technology and other gizmos.
But, we tend to forget that great builders, like the Romans for example, constructed roads, sewers, aqueducts, bridges, structures, without lasers and computers. Their works have stood for centuries. And, imagine doing math with Roman numerals! They even had rudimentary cranes and understood gearing. They could do a lot of things we do now, but just didn’t have power machinery to do it.
For a great look at ancient building techniques, read the Roman author and architect, Vitruvius, who wrote [De architectura](https://en.wikipedia.org/wiki/De_architectura).
There’s a misconception that ancient and even recent past is super primitive compared to our modern (as of 2019) knowledge and tech, but people have been super innovative and resourceful for several thousand years. Just the last 10-20 years have probably doubled our knowledge of the total so far…
There’s a lot of talk about protractors and string here … that’s only partly right. Traditional survey instruments (same principles often used today) measured angles, horizontally and vertically, extremely precisely. Quick precise distance measurement came later, but one carefully measured baseline and a series of intersecting angles can coordinate points better than you’d expect.
GPS isn’t as useful as you’d think for surveying in closed-in or covered areas, so we still use similar instruments almost every day. Behind all the software, modern terrestrial survey instruments still just measure horizontal angles, vertical angles, and slope distances.
Leveling is even easier! In fact, if you want to be really basic, you can even do it with water.
Source: professional land surveyor.
laser measuring? I can build you a bridge with 100 feet of rope, a hatchet, and a few* pitchers of lemonade
They did pretty much what I did when I built a fence around my house:
* Put a stick at either end.
* Have someone at one of the sticks, looking so that both sticks line up.
* Have someone else put remaining sticks in a line between them, lining up the top of the sticks with that sight line.
Accurate to within a millimeter or so, if done carefully.
Sure, they probably didn’t line up sticks, but the principle remains. With two set points, one at each end, it’s very easy to accurately put stuff on a straight line between them.
String. They lined up string measured by levels and squares. Also stone masons back then were absolutely ace when it came to construction. Roman masonry work still functions in some places after 2020 years.
To blow your mind, the middle of this bridge washed out and they rebuilt it. It has a bit of a kink now. Steel beam suspension bridge. https://www.newspapers.com/clip/31159286/palmer_st_bridge_august_21_1955/. https://en.m.wikipedia.org/wiki/Northampton_Street_Bridge
Even more impressive is the transcontinental railroad, one of the tunnels they dug out from both sides and met up in the middle. They were within an inch I think
I’d ask the same question about *tunnels*. You can’t even see where you’re headed.
IIRC there’s some tunnel connecting Manhattan with either New Jersey under the Hudson River or Brooklyn under the East River (I don’t remember what side) that was built in the late 1800s with two excavation teams from both sides that met in the middle with an error of less than 1 inch. I can’t get through my skull how this could be done at the time.
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