Aqueducts
Supplying water constantly to roman citizen all the time using Aqueducts is one of the most remarkable engineering feat. The roman's had the ability to supply fresh water using gravity and engineering expertise from almost 7 miles or more distance away from city.
This idea of providing water from far distance to city center was far advanced from their time. The only tools to achieve this significant goals were their basic hand tools digging tunnel through mountains and establishing stone structures high above (as shown in the video below and picture on right) .