# Why did the Romans bother to build aquaducts? **URL:** \ **Category:** Factual Questions\ **Created:** [January 6, 2011, 1:28pm UTC](https://boards.straightdope.com/t/why-did-the-romans-bother-to-build-aquaducts/566602 "2011-01-06T13:28:26Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Schnitte](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/schnitte/32/9033_2.png) [@Schnitte](https://boards.straightdope.com/u/Schnitte)\ **Post date:** [January 6, 2011, 1:28pm UTC](https://boards.straightdope.com/t/why-did-the-romans-bother-to-build-aquaducts/566602/1 "2011-01-06T13:28:26Z")
Obviously to get water from the source to the cities where it’s consumed, I know. But the whole point of an aqueduct is to have a line with a constant slope, to ensure that the water will flow unimpeded - if this requires the line to be raised to a level above that of the surrounding ground, then you need to build an aqueduct. Yet, the constant slope thing is unnecessary. The law of communicating vessels, which is attributed to Archimedes and thus should have been well known to the Romans, means that, as long as one end of the line lies higher than the other, water will flow from the latter to the former even if the line goes up and down in between. This makes it possible to build a simple ground-level pipeline, eliminating the need for the expensive bridge structures we know as aqueducts. So why did the Romans bother to build them nonetheless? Did they have problems to make pressurised tight pipes? Was it worry that a ground-level line would be susceptible to sabotage? Or did they simply not make the mental leap of putting a law known to their phycisists into engineering application? ---
**Author:** ![Ludovic](https://avatars.discourse-cdn.com/v4/letter/l/7ab992/32.png) [@Ludovic](https://boards.straightdope.com/u/Ludovic)\ **Post date:** [January 6, 2011, 1:39pm UTC](https://boards.straightdope.com/t/why-did-the-romans-bother-to-build-aquaducts/566602/2 "2011-01-06T13:39:57Z")
Sometimes they [did](http://en.wikipedia.org/wiki/Aqueduct_of_the_Gier) use pressurized pipes to get across a particularly difficult valley. I’d have to guess that for the other situations, digging a tunnel was just easier. ---
**Author:** ![mbh](https://avatars.discourse-cdn.com/v4/letter/m/a6a055/32.png) [@mbh](https://boards.straightdope.com/u/mbh)\ **Post date:** [January 6, 2011, 1:42pm UTC](https://boards.straightdope.com/t/why-did-the-romans-bother-to-build-aquaducts/566602/3 "2011-01-06T13:42:43Z")
> [@](#): > > Did they have problems to make pressurised tight pipes? This. The law of communicating vessels is lovely in theory. Getting it to work properly in the real world is a nontrivial engineering problem. Especially with bronze-age technology. The nice thing about aqueducts is that they don’t need to be airtight or pressurized. ---
**Author:** ![Quercus](https://avatars.discourse-cdn.com/v4/letter/q/7ab992/32.png) [@Quercus](https://boards.straightdope.com/u/Quercus)\ **Post date:** [January 6, 2011, 1:46pm UTC](https://boards.straightdope.com/t/why-did-the-romans-bother-to-build-aquaducts/566602/4 "2011-01-06T13:46:16Z")
> [@Schnitte](#): > > Did they have problems to make pressurised tight pipes? I’m guessing this. Metal was much, much, scarcer in Roman times. I imagine making pressure-tight pipes out of stone is pretty difficult (at least over any distance). Also pressure-tight pipes require a lot more maintenance and tend to fail catastrophically, wheras a leaking sloped aqueduct just loses some water. ---
**Author:** ![Keeve](https://avatars.discourse-cdn.com/v4/letter/k/f07891/32.png) [@Keeve](https://boards.straightdope.com/u/Keeve)\ **Post date:** [January 6, 2011, 1:51pm UTC](https://boards.straightdope.com/t/why-did-the-romans-bother-to-build-aquaducts/566602/5 "2011-01-06T13:51:48Z")
> [@Schnitte](#): > > Did they have problems to make pressurized tight pipes? That’s my guess. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [January 6, 2011, 2:17pm UTC](https://boards.straightdope.com/t/why-did-the-romans-bother-to-build-aquaducts/566602/6 "2011-01-06T14:17:20Z")
Pipes were not unknown to the Romans - we get the word ‘plumbing’ from them - but that word in turn derives from the Latin word for Lead (plumbum). Lead isn’t a particularly strong material, so I would imagine pressure inside ordinary lead pipes (at least the kind the Romans used) could be a problem. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [January 6, 2011, 2:21pm UTC](https://boards.straightdope.com/t/why-did-the-romans-bother-to-build-aquaducts/566602/7 "2011-01-06T14:21:01Z")
Anyway. A slope isn’t necessary in an aqueduct either. It improves the rate of flow, but is not essential. ---
**Author:** ![CalMeacham](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/calmeacham/32/35_2.png) [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)\ **Post date:** [January 6, 2011, 2:24pm UTC](https://boards.straightdope.com/t/why-did-the-romans-bother-to-build-aquaducts/566602/8 "2011-01-06T14:24:17Z")
Roman _sewage_ plumbing used glazed ceramic tile. my suspicion is that they used aqueducts for water supply not only because of metal shortage, but because of maintenance. Not only don’t aqueducts require no sealing to work, they don’t corrode and are relatively low maintenance – no small thing in maintaining a system over the years. It also guarantees a pressure “head” without the necessity of having a water tower and a pump system to get it up there. Lindsay Davis, in _Three Hands in the Fountain_, one of her Marcus Didius Falco mystery novels set in Titus-era Rome, describes him going into the Roman water system. I don’t know how fully she researched it, but it has a ring of truth – rickety ladders used for access and portions of the water system silted up with sand and soil brought down by the waters. I could see all of that rapidly clogging up a metal pipe system, and being a real bitch to clean out, whereas with an open-air aqueduct you just need some guys with shovels. ---
**Author:** ![Koxinga](https://avatars.discourse-cdn.com/v4/letter/k/4af34b/32.png) [@Koxinga](https://boards.straightdope.com/u/Koxinga)\ **Post date:** [January 6, 2011, 2:27pm UTC](https://boards.straightdope.com/t/why-did-the-romans-bother-to-build-aquaducts/566602/9 "2011-01-06T14:27:11Z")
Aren’t there still a handful of Roman aquaducts still in use? If so, that shows their solution was nothing to sneeze at. ---
**Author:** ![Keeve](https://avatars.discourse-cdn.com/v4/letter/k/f07891/32.png) [@Keeve](https://boards.straightdope.com/u/Keeve)\ **Post date:** [January 6, 2011, 3:07pm UTC](https://boards.straightdope.com/t/why-did-the-romans-bother-to-build-aquaducts/566602/10 "2011-01-06T15:07:05Z")
> [@Mangetout](#): > > Anyway. A slope isn’t necessary in an aqueduct either. It improves the rate of flow, but is not essential. I presume you mean that it can be horizontal, and does not have to slope downhill. Surely you’re not suggesting that an uncovered aqueduct can go uphill, as the OP would have needed? ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [January 6, 2011, 3:37pm UTC](https://boards.straightdope.com/t/why-did-the-romans-bother-to-build-aquaducts/566602/11 "2011-01-06T15:37:54Z")
> [@Keeve](#): > > I presume you mean that it can be horizontal, and does not have to slope downhill. Yes. > [@](#): > > Surely you’re not suggesting that an uncovered aqueduct can go uphill, as the OP would have needed? No, I was just addressing the ‘constant slope’ thing, although I guess a level aqueduct is just one with a constant slope of zero. ---
**Author:** ![Schnitte](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/schnitte/32/9033_2.png) [@Schnitte](https://boards.straightdope.com/u/Schnitte)\ **Post date:** [January 6, 2011, 3:43pm UTC](https://boards.straightdope.com/t/why-did-the-romans-bother-to-build-aquaducts/566602/12 "2011-01-06T15:43:34Z")
> [@Koxinga](#): > > Aren’t there still a handful of Roman aquaducts still in use? If so, that shows their solution was nothing to sneeze at. I’m not saying their solution was not functional. I’m just asking if they could not have achieved the same, or at least a lower but still satisfactory, level of functionality more easily or cheaply with ground-level pipes. ---
**Author:** ![Koxinga](https://avatars.discourse-cdn.com/v4/letter/k/4af34b/32.png) [@Koxinga](https://boards.straightdope.com/u/Koxinga)\ **Post date:** [January 6, 2011, 3:45pm UTC](https://boards.straightdope.com/t/why-did-the-romans-bother-to-build-aquaducts/566602/13 "2011-01-06T15:45:54Z")
> [@Schnitte](#): > > I’m not saying their solution was not functional. I’m just asking if they could not have achieved the same, or at least a lower but still satisfactory, level of functionality more easily or cheaply with ground-level pipes. In terms of lifetime total cost, including maintenence and replacement, I think the answer’s still no. ---
**Author:** ![Rigamarole](https://avatars.discourse-cdn.com/v4/letter/r/77aa72/32.png) [@Rigamarole](https://boards.straightdope.com/u/Rigamarole)\ **Post date:** [January 6, 2011, 4:18pm UTC](https://boards.straightdope.com/t/why-did-the-romans-bother-to-build-aquaducts/566602/14 "2011-01-06T16:18:13Z")
When you have an endless supply of slave labor, there’s no reason not to go all out. ---
**Author:** ![Exapno\_Mapcase](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/exapno_mapcase/32/1051_2.png) [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)\ **Post date:** [January 6, 2011, 4:24pm UTC](https://boards.straightdope.com/t/why-did-the-romans-bother-to-build-aquaducts/566602/15 "2011-01-06T16:24:52Z")
> [@Rigamarole](#): > > When you have an endless supply of slave labor, there’s no reason not to go all out. Slaves were used extensively, but so were paid laborers and even the legions when they would otherwise be idle. Aqueducts were a huge and endless infrastructure project. It’s hard to make a single generalization stick. ---
**Author:** ![Malthus](https://avatars.discourse-cdn.com/v4/letter/m/85f322/32.png) [@Malthus](https://boards.straightdope.com/u/Malthus)\ **Post date:** [January 6, 2011, 4:31pm UTC](https://boards.straightdope.com/t/why-did-the-romans-bother-to-build-aquaducts/566602/16 "2011-01-06T16:31:00Z")
> [@Mangetout](#): > > Yes. > > No, I was just addressing the ‘constant slope’ thing, although I guess a level aqueduct is just one with a constant slope of zero. The reason for a constant slope, aside from having a better flow for the user, was I understand to avoid silting. A place where there was a level would tend to silt up over time, or so I’ve read, so you want them to be as few as possible. ---
**Author:** ![Jim\_s\_Son](https://avatars.discourse-cdn.com/v4/letter/j/e19adc/32.png) [@Jim\_s\_Son](https://boards.straightdope.com/u/Jim_s_Son)\ **Post date:** [January 6, 2011, 5:24pm UTC](https://boards.straightdope.com/t/why-did-the-romans-bother-to-build-aquaducts/566602/17 "2011-01-06T17:24:51Z")
By using the legions, you kept them busy doing things instead of plotting how to overthrow the emperor and put their own commander in office to get bonuses (which happened often enough as it as). Military minds love make-busy work. ---
**Author:** ![Philster](https://avatars.discourse-cdn.com/v4/letter/p/13edae/32.png) [@Philster](https://boards.straightdope.com/u/Philster)\ **Post date:** [January 6, 2011, 5:59pm UTC](https://boards.straightdope.com/t/why-did-the-romans-bother-to-build-aquaducts/566602/18 "2011-01-06T17:59:55Z")
Too much slope is bad, too. Too little _or_ too much sloping can leave solids behind to cause clogs. Too much slope might cause the water flow to run to shallow for too long to properly suspend (and move) debris (i.e., if you wish debris/silt to move along). ---
**Author:** ![Man\_With\_a\_Cat](https://avatars.discourse-cdn.com/v4/letter/m/cab0a1/32.png) [@Man\_With\_a\_Cat](https://boards.straightdope.com/u/Man_With_a_Cat)\ **Post date:** [January 6, 2011, 6:43pm UTC](https://boards.straightdope.com/t/why-did-the-romans-bother-to-build-aquaducts/566602/19 "2011-01-06T18:43:58Z")
> [@CalMeacham](#): > > … > > It also guarantees a pressure “head” without the necessity of having a water tower and a pump system to get it up there. One of my favorite memories from college was the sound of 40 people completely losing it when our female professor kept saying “total dynamic head”. Hey, we were 18, it was funny. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [January 6, 2011, 7:40pm UTC](https://boards.straightdope.com/t/why-did-the-romans-bother-to-build-aquaducts/566602/20 "2011-01-06T19:40:51Z")
The [Aqueduct of Segovia](http://en.wikipedia.org/wiki/Aqueduct_of_Segovia) is 93 ft tall. If they’d used a pressurized pipe instead, the pressure at the bottom of the valley would have been 40 psi. That’s not a trivial pressure to deal with. [Next page](https://boards.straightdope.com/t/why-did-the-romans-bother-to-build-aquaducts/566602.md?page=2)