I have always been fascinated by ancient Rome. I guess, foremost by the ancient engineering and the state of the Roman civilization, in regards to the infrastructure and the technology.
One of the most intriguing Roman structures must be the Aqueduct. Although these are very much associated with the Romans, aqueducts were devised much earlier in the Near East and Indian subcontinent. The fact that Romans often get away with the credit is that all across Europe, in the parts of the former Roman Empire, one can find very well preserved remains of these spectacular architectural achievements. Some Roman aqueducts are actually still in use, although I found conflicting information about which ones indeed are. The two millenia old aqueduct in Segovia, Spain was at least still in use fifty years ago, supplying the city with water. And the renowned Fontana di Trevi in Rome does receive today water from a modernized ancient aqueduct called Aqua Virgo.
One of the most beautifully preserved and famous is Pont du Gard in France. It was built circa 19 BC and is today a World Heritage Site. Although it is by now suffering from the tides of time and is unfortunately in a great danger of collapsing in the near future.
Roman aqueducts were extremely sophisticated constructions. They were built to transport water inside the arches, within small channels across the Roman Empire, supplying city fountains and baths with fresh water. The principle is very simple - the aqueduct is constructed in such a way that it is titling or leaning in a very shallow gradient of remarkably fine tolerances. For example, at the Pont du Gard, this gradient accounts of only 34 cm per km, descending only 17 m vertically in its entire length of 50 km (31 miles). This is absolutely incredible, as to the naked eye the structure appears completely horizontal. The challenge of an aqueduct was to get this gradient right, because it would overflow or clot if not. Powered entirely by gravity, it could carry large amounts of water very efficiently. The Pont du Gard could transport up to 20,000 cubic meters — nearly 6 million gallons — a day, and the combined aqueducts of the city of Rome supplied around 1 million cubic meters (300 million gallons) a day.
Considering the absolute simplicity behind the concept of the construction, combined with an impeccable building precision, these structures are to me as astounding as any of the seven wonders of the ancient world.