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Comment by AngryParsley | Hacker News Reader

The Pantheon is awesome, but one shouldn't think, "They don't make 'em like they used to."

Almost all structures built 2,000 years ago do not exist today. The ones that do exist are all marvelous feats of engineering because if they weren't, they wouldn't have stuck around for 2,000 years. I guess it's an example of http://en.wikipedia.org/wiki/Survivorship_bias

OK, back to gawking at the Pantheon. It's absolutely stunning that people could build such a dome using 5,000 tons of concrete, no steel, and no power tools.

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For this to be the case you would have to assume that the main reason that a 2,000 year old building is not around is because it fell down due to structural flaws. I think in Rome and Athens there is a lot of evidence that people knocked their houses down to build something fancier, or they were destroyed during war or civil unrest.

So it's not a simple case of survivorship bias, though undoubtedly that is one factor.

No, you wouldn't have to assume that. All the alternative factors you mention can tear down a sound building, but none of them can help an unsound one survive 2000 years.

A building that lasts that long is robust almost by definition. So, as long as any buildings do survive, we have fertile soil for survivorship bias.

I don't think you are applying the statistical notion of survivorship bias completely accurately.

The original comment questioned the accuracy of the statement "they don't build them like they used to", which I took to refer to building standards 2000 years ago.

Consider the following two scenarios:

A. 2000 years ago, all buildings were shoddily engineered except the Pantheon.

B. 2000 years ago, 90% of buildings were well engineered, of which the Pantheon is one example. The rest were deliberately torn down for one reason or other.

Survivorship bias does not allow you in itself to distinguish between A and B, which is the interesting question. It just allows you to disprove C:

C. Since the Patheon still stands, all buildings 2000 years ago must have been brilliantly engineered.

Which nobody is arguing for, I don't think.

Thats a great point. All the Model Ts still rolling have incredible longevity but millions of them have been gone for many decades.

My initial reaction was that 'millions' must be an exaggeration here. Surely, I thought, there were far fewer than a million cars sold that early. But I would have been wrong: "From 1908 to 1927 Ford produced more than 15 million Model T automobiles." http://www.modelt.ca/faq.html#2

Thanks for the good example!

i spent some time looking at the local newspaper archives, it is astounding in 1900~1910, all photos go from being devoid of cars to being exclusively cars

you bet!

I'm always amazed by the Egyptians. They cut enormous obelisques(sp?) out of solid rock, rolled them onto enormous barges, floated them down the Nile, then erected them (pun intended) with nothing more than rope, sweat, logs and dirt. Pretty awesome stuff really.

Just goes to show you how powerful bread is. Egypt had great harvests on a regular basis, something few other places could accomplish, so they were able to spend more time developing knowledge. "Western Civilization" was born in Egypt, don't let anyone tell you different.

Also, a three mile long ramp.

A three mile long ramp made of dirt. I said they used dirt. Dirt.

I like to ask my students how they think the Egyptians did stuff like this. They usually guess something like "a wooden thing with rope and they pulled it up." It's hard to comprehend how much effort Egyptians put into their projects. Building an enormous ramp and then tearing down an enormous ramp? That's a lot of shoveling.

When you have a large number of slaves lots of things that would normally be impossible suddenly becomes easy.

However egyptologists today believe that slaves weren't the force behind building pyramids etc.

http://en.wikipedia.org/wiki/Egyptian_pyramid_construction_t...

Except that they have found archaeological evidence that shows that ramps were used to build some pyramids, such as the Great Pyramid of Giza[1].

And from your wiki page: Most Egyptologists acknowledge that ramps are the most tenable of the methods to raise the blocks...

1. http://www.bbc.co.uk/history/ancient/egyptians/great_pyramid...

Why "except"? My point was that the workers were not slaves. Ramps are certainly the most probable aid in construction.

Hm, not sure. When I posted, I think I may have had you and bloomshed mixed up. He was expressing some skepticism about a ramp being used to build pyramids. Sorry about that!

I didn't mean to sound like I was being skeptical about ramps. Ramps make the most sense, especially the enormous three mile ones that lead right to the top level of the pyramid being built. I love big ramps made of dirt!

Egyptians also used the "build an earthen ramp to get the heavy stuff up, then clear the dirt away after you're done" strategy to build their ridiculously awesome temples. Any History Channel fan knows that.

The lack of power tools may have exactly been why the building is as sturdy as it is. It took the builders several years to build the whole building. Most of the concrete they used hardened out before they built on the next section.

If they would have had powertools, construction would have progressed a lot faster, the concrete would not have hardened as well as it should and the building would have cracked and collapsed a lot more easily.

Plenty of shoddily constructed buildings were also made without power tools.

There might be an element of truth to your argument, but I suspect the more important factor is the influence of the party motivating the construction.

A Roman businessman building a hi-rise tenement building would probably not bother enforcing the use of quality engineering and materials. They also didn't use power tools, but if I'm not mistaken, these hi-rise apartment blocks were known to collapse.

But if you're building something like the Pantheon, in Rome, for the emperor Hadrian, you're going to have access to the best materials, and are not going to want to risk your neck by slacking.

The fact that a building survives for 2000 years isn't necessarily a 'marvelous feat of engineering'.

It might just be that the architect accidentally designed something strong enough. For example, many Gothic cathedrals collapsed during construction, and the ones still standing often are way stronger than needed.

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