How the Colosseum was built and why it was an architectural marvel

cement is the binder, usually made of lime, which is mined from limestone.

concrete is cement plus other materials such as gravel.

stones are naturally forming solids made from minerals.

this should help get you started. wikipedia is your friend.

Concrete is a human-made agglomerate of a filler (usually sand), a binder (nowadays usually Portland cement, the Romans used lime) and an aggregate (gravel, crushed granite, crushed old concrete, ...) which cures to a solid. It can be poured as a slurry, formed as a paste, dry-pressed and hydrated (concrete roof tiles are made this way), sprayed, injected and more - i.e. it is a versatile material.

The difference between cement and concrete is the difference between boiled linseed oil and paint in that cement is the binder for making concrete while boiled linseed oil is the binder for (traditional) paint. It is what keeps the other ingredients (filler and aggregate for concrete, pigments for paint) together.

Stone is a portmanteau for the material from which rock is made, this can include sedimentary conglomerates like sandstone, metamorphics like soapstone, igneous extrusives like basalt, igneous intrusives like granite and more. In short, it is the hard mineral stuff rocks are made off.

The "setting" you refer to is the time it takes for the binder(s) to react to produce the final agglomerate, not the shape into which it sets. It would be possible to shape basalt by pouring lava (i.e. molten rock) into a heat-resistant form, going from hot to cold to create the final product. It is also possible to sinter ceramics at high temperature in some desired form, going from cold to hot to cold. Since there are no ovens big enough to sinter buildings this tends to be limited to smaller parts, e.g. refractive (heat-resistant) stones for building hearths etc.

Concrete is made up of both cement (the CONtinuous part) and aggregate/stone (the disCRETE part), so cement vs concrete is kind of like broth vs soup, and concrete and stone like soup vs vegetables.

> So the main difference is that you can shape it without chiselling it.

I guess, yeah. Both are really good at withstanding compressive forces. Unlike Roman times, concrete today is usually reinforced with steel rebar, which gives it good tensile strength as well. This makes it useful for a lot of things that stone is not.

Disclaimer, take everything here with a grain of salt. Continuous-discrete is not the etymology of concrete. This might help too: https://youtu.be/UOHURuAf5iY

You essentially got the concept right, concrete is essentially artificial stone that can be initially poured into a mould and once set has characteristics similar to some types of stone.

Concrete is a mix of elements with different sizes (granulometry), like sand, gravel, (crushed) rock (of various sizes), with one or more binding agents, it is a "conglomerate" (in quite a few languages concrete is properly called the equvalent "cement conglomerate", in English "conglomerate" designs a natural rock that shares the same kind of structure:

https://en.wikipedia.org/wiki/Conglomerate_(geology)

Cement is just the most used binding agent, usually very, very fine.

As a comparison, what is usually called asphalt is another kind of conglomerate where the binding agent is bitumen.

Cement by itself has very good hardness but it is fragile and/or brittle (and it has very relevant shrinking when setting).

Mortar is cement+sand, it is a sort of midway between the two.

Stone (it depends on which kind of stone we are talking) is ultimately a sort of natural concrete where the particles (that may also be monogranular) have been "assembled" by pressure (and heat) over countless time.

Typically stone is quarried from very huge monolithic deposits, or it comes in large slabs, that are cut to make (transportable) bricks or samller slabs, that you then assemble with mortar.

Chiseling is not involved in building with stone (anymore) if not for decoration/aesthetic reasons.

Whether casting concrete or assembling stone elements in - say - a wall is faster or slower it is hard to say, it greatly depends on the structure, on the available tools/equipment and local costs for the one or the other and for the labour, usually concrete is cheaper because the components cost less, the tools and equipments are readily available and there is less labor involved, but it depends on the specific place/country.

In the case of reinforced concrete, the advantage is that you can make much thinner structures with same or better structural strength than masonry.

Structural engineer here. Much of what is said in the other responses is correct, but I will try to explain it as structural engineers do and also use industry-standard terms.

There are many things called concrete. I am going to use the word "concrete" to mean "Portland cement concrete". That's what you are describing in your questions.

Concrete is the stuff sidewalks are made of. Some people use the word "cement" when describing sidewalks. But that is akin to calling bread yeast. Sure, there is cement in concrete like there is yeast in bread but concrete is more than cement as bread is more than yeast. Cement and yeast are the active ingredients only.

Hardened concrete is a composite material made up of aggregates and a binding matrix that holds the aggregates together. Aggregates in concrete include sand (fine aggregate) and gravel or crushed stone (course aggregate). The matrix consists of cement particles and minerals that grow out of those particles as the cement reacts with water: a process we call hydration. These minerals or "hydration products" grow around the aggregates and give the concrete its strength.

What we call cement is rightly called Portland cement. It is added to a concrete mix in the form of a very fine powder. The cement is manufactured from limestone (primarily) that has been fired in a kiln before being ground to that extremely fine powder. The kiln treatment is how it becomes hydraulically reactive.

Material that reacts with water similar to Portland cement also occurs naturally around volcanoes. I believe that is where the Romans got the cement for their concrete. But nowadays we manufacture Portland cement it instead.

Hardened concrete is strong in compression (when squeezed) but weak in tension (when pulled apart). When we need tensile strength, we add steel reinforcement. The resulting composite material is referred to as reinforced concrete. Concrete can also be used without steel reinforcement when it is not subject to tensile loads. This we call either plain concrete or unreinforced concrete.

The word "rock" or "stone" encompasses a wide range of naturally-occurring solid materials made up of various minerals. Limestone, granite, marble, and sandstone are common examples. Most of the solid rock you see around your world is much stronger than concrete. Concrete is an imitation of rock. In fact, the name Portland cement was given to it because the concrete resulting from its use supposedly looks similar to natural stone quarried on the Isle of Portland in the United Kingdom.

I hope this helps. In short: Portland cement, water, and aggregate (sand and crushed natural rock or gravel) are mixed or "batched" and harden by a chemical reaction called hydration to produce a solid material similar to natural stone but with many practical advantages over rock.

You've probably heard this already but go to see the Trevi fountain - it's just there in the streets, you don't need a ticket; and in fact, a walkabout of that whole area is beautiful.

I also really enjoyed an afternoon walking around St Peter's Basilica in Vatican City - the museum is stuffed to the gills with ancient relics that the catholic church 'collected' from around the world, and the architecture of the building itself is awe inspiring.

The Sistine chapel and Vaticans Museums at least once in a lifetime. I suggest taking a guided tour and book in advance (as everything in Italy).

Pantheon.

The inside of the st Peters basilica was probably one of the most awe inspiring things I have ever seen. And I'm saying that as an atheist purely appreciating the architecture and scale of the insides.

Roman here.

The historical area in the city center is much bigger than people think, it could take 3/4 days just walking around to see everything, without stopping for a visit, so take that into account.

Also, it's pretty hot right now (around 35-37 degrees Celsius), mind that too.

I won't give you the usual list of monuments and such, you can find all about them in any travel guide or IG/tik tok account, but don't miss the visit to Colosseum and the forum (especially the forum),book tickets in advance it'll save you a lot of time at the ticket office under the sun, do the same if you thought about visiting the Vatican museums.

A spot that's not usually under the radars is Terrazza Caffarelli (https://www.terrazzacaffarelli.it/) on top of Campidoglio (Capitoline Hill), you'll find a nice rooftop bar there with a beautiful view.

Edit: I totally forgot about the Museum and Crypt of Capuchins in Via Veneto, there's a San Francesco painting by Caravaggio and, if you are not disturbed by that stuff, a crypt entirely decorated with monks' bones and skulls. There are literally hundreds of them and thousands bones. It's pretty unusual, but kinda great if you ask me.

I'm biased because I live there, but if you wanna eat near the Colosseum my advice is to try Taverna Romana for roman recipes and Tettarello for pizza. Those are two of my favorite places to eat in Rome in general.

I don't know how long are you staying but if you get the chance go to the beach one day. The south is the best, especially Sabaudia that is just below Odyssey's famous Mount Circeo, but you gonna need a car to go there.

https://www.viaggiando-italia.it/wp-content/uploads/2022/03/...

Anyway, enjoy the visit!

Buy your tickets in advance online for everything that requires a ticket in Rome, especially if you want to step onto the Colosseum arena (it’s a separate ticket from the general admission). Same with Vatican Museums and Sistine Chapel. Everything sells out quickly.

Carciofi alla giudia, but I think the season for artichokes has just ended. Check for the right restaurants well: there are thousands of Professionals, yet also the complication and noise of the temptation from tourism (i.e. literal customers ("customary customers") mandate and, conversely, fleeting visitors tempt into laxity and "for the stakeholders" business ways).

The City: walk around a lot, with pace, enjoy the corners. Notice the palaces. Enjoy the big and the small. Most of the City is an open museum.

Notice: what about seeing in the evening an artist with a canvas under his arm in conversation with the antiques dealer in front of his shop, the living Culture physically moving in the streets? Were Italy properly managed, Italy would be everything.

If you want to visit St. Peter in the vatican, it's free, but there can be significant waiting time for entry. But you can rent an audio guide (online in advance) and skip the line.

Similarly, if you want to visit any museums, especially the vatican museums, book in advance and skip the lines.

Ostia Antica is worth a visit. It's the lost and "sunken" harbour city of ancient rome. You can roam there freely and explore a ruined city and discover 2000 year old mosaics and wall art.

Romans (and italians in general) like to eat late in the evening. So if you want to go out for dinner, but have no reservation, you can try to arrive early (6pm) at the restaurants or pizzerias and tell them, that you are just interested in some quick dinner and will be gone before their "regular" patrons arrive. That usually works.

If you need to drive a car in Rome: Don't. If you must, avoid the oldest parts of the city with the narrow streets.

The Colosseum had until recently night tours, but I think were suspended due to the pandemic. Might want to check out what options they have now.

Also, if general admission tickets for the Colosseum are sold out check for tour tickets in specific languages. Those are almost never sold out and you don’t have to stick with the tour guide ;)

Stay away from restaurants with a “view”, they tend to be tourist traps. Google reviews are very helpful here.

And last, check the menu prices vs. the receipt charges. I was unfortunately hustled a couple times, never for more than 10 or 15 euros, but it made the experience sour a bit.

You’re going to have an excellent time no matter where you go. It’s Rome!

The one place?

Sistine Chapel.

Kind of like the Grand Canyon, in that there's nothing else of similar magnitude in the way the thing is big.

One memorable site is the Church of Saint Clement (Basilica San Clemente). What makes it remarkable are excavations which have revealed so much more than the 12th century church on ground level. Below it is another church from the 4th century. Below that, Roman buildings from the 1st century. So much history on one small site, descending through various stages human settlement below. Giving a taste of what has been repeated over much of the city for millennia.

The underground parts of the Colosseum require special tickets for entry so make sure you get those ahead of time if you want to see those.

In the nearby Forum, look for the Temple of Caesar which is where Caesar's body was cremated and don't miss the Palatine Hill Viewpoint overlooking the Forum.

Across town, don't miss the Pantheon, the nearby Curia of Pompey where Caesar was assassinated, and the statue of Giordano Bruno.

Get on the walking tour. If the tall handsome blond man Paolo is doing it then lucky you. Until you do the tour you cannot imagine how much context you'll miss just by walking around on your own.

I think I read that something like half a million people died in the shows at the colosseum. Imagine the reputation it must have had while it was operating - like a real-world version of The Running Man.

You should very certainly reinstate representative democracy: where you vote for a candidate and are systemically entitled to reasonable direct relation with them. (You know, what was in place before. Let us not dwell into uncomfortable details.)

And complain directly through the open channels.

Or, create pressure groups.

Wild boars in the city? Really?

No, at that link one can find only the table of contents.

If size is the only thing that matters to you in a building or structure, I guess you'd admire the Burj Khalifa. Although, incidentally, that's also a bit of an engineering marvel. Perhaps start with something simpler, the Pentagon or something like that. Pretty large.

Just in case readers are confused by this: it's not really small.

It's also really run down, you'd think they could afford to fix it up a bit!