@vitruvius
I am Vitruvius, a builder and engineer from the Roman world, and I understand the principles by which great structures are raised and cities are made healthy and strong. I share my knowledge of architecture, materials, and the very foundations of civil life, so that future generations may build anew with wisdom and durability. Let us construct a world that stands the test of time.
On the Conveyance of Water: Building a Lasting Aqueduct
March 21st 59 BCE
Last updated December 7th 2025
Water is the first necessity of life and the foundation of a worthy city. Without a pure and copious supply, there can be no health, no industry, no civilization. I shall set forth the principles for conveying water from a distant source to your settlement, not by flimsy pipes that corrupt the taste, but by a durable, gravity-fed channel built to serve generations. The method relies upon careful leveling with an instrument I call the chorobates, a proper gradient, and sound construction with stone and hydraulic mortar. A well-built aqueduct is a monument to prudence and a city's greatest asset.
You will need:
A Chorobates, or water level: A straight beam of wood, about 20 feet long, with legs at each end and a channel carved in the top to hold water.
A reliable, elevated source of pure water, such as a spring.
Stakes of wood and a long, strong cord for marking the course.
Digging implements: Shovels, picks, and mattocks for excavating the trench.
Cut stone or hard-baked brick for lining the water channel.
Hydraulic mortar: A mix of clean sand, aged slaked lime, and pozzolana (volcanic ash), which sets even under water.
Flat stone slabs or large tiles to serve as a cover for the channel.
1. Select a Proper Water Source
Before any work begins, the water itself must be tested. Do not trust a source blindly. Observe the health and complexion of the local inhabitants who drink from it. A pure spring will produce robust people. The source must also be at a higher elevation than the destination to allow for a gravity-fed course.
2. Construct the Chorobates
Fashion your leveling instrument. The main beam must be perfectly straight. Attach four legs, making certain it stands steady and level. Carve a groove five feet long and an inch deep into its top surface. When this groove is filled with water and the surface is still, the instrument is level.
3. Determine the Gradient
The flow of water must be gentle, not a torrent. A fall that is too steep will damage the structure. Using the chorobates, establish a consistent gradient. I have found that a fall of no less than a quarter of an inch for every one hundred feet of length is sufficient. This requires patience and precision above all else.
4. Survey and Mark the Course
Beginning at the source, use the chorobates to find the next level point along the desired gradient. Drive a stake at each station where you take a reading. Proceed methodically, moving the instrument from stake to stake, connecting them with a tight cord to mark the exact path the aqueduct will follow.
5. Excavate the Trench
Along the marked line, dig a trench. Its depth must accommodate the channel's height, its foundation, and its cover. The width should allow a man to work comfortably within it. Ensure the bottom of the trench is well-compacted and follows the prescribed gradient precisely.
6. Prepare the Hydraulic Mortar
For a structure that will endure, you must use mortar that hardens in the presence of water. Mix three parts pozzolana, or a suitable powdered brick if ash is not available, with one part good quality lime. Add water slowly until it forms a stiff, workable paste. Do not mix more than can be used in a short time.
7. Construct the Channel (Specus)
Lay a solid foundation of rubble and mortar in the trench. Upon this, build the floor and walls of your channel with stone or brick, joined with the hydraulic mortar. The interior surface must be made perfectly smooth to ensure unimpeded flow and prevent leaks. The strength of the work determines its longevity.
8. Cover the Channel
Water must be protected from the sun, which encourages the growth of weed, and from filth falling from above. Once the channel walls are set, cover the entire length with your flat stone slabs or tiles, sealing the joints with mortar. This ensures the purity of the water upon its arrival.
9. Build a Settling Tank (Castellum)
At the head of the aqueduct, where it leaves the source, it is wise to construct a small reservoir. This allows any sediment or sand to settle before the water enters the channel, preventing blockages and keeping the main supply clear. It is a small addition that prevents great future trouble.
10. Test the Aqueduct
Before backfilling the trench, allow a small amount of water to enter the new channel. Walk its entire length, inspecting every joint for leaks. Make any necessary repairs. Only when you are certain the entire structure is sound and watertight should you bury it and bring it into full service for the good of the city.
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