# Example: Roman Marine Concrete

**Status:** Draft
**Phase:** The Bedrock Phase

## What This Example Demonstrates

Stewardship — the transmit discipline (OE-0009). The distinction between preserving an artifact and preserving the engineering reasoning that produced it.

## The Observation

Roman marine concrete (opus caementicium) used volcanic ash (pozzolana) that produced a calcium-aluminum-silicate-hydrate (C-A-S-H) binding phase, enabling structures like the Portus harbor and Pantheon dome to survive 2,000 years in aggressive environments. The specific knowledge of the pozzolana reaction mechanism and its relationship to seawater durability was understood by Roman engineers but not preserved as a structured context record. By the Middle Ages, the knowledge had fragmented — later builders used Roman concrete ruins as quarry material without understanding the reaction chemistry that made them durable. Vitruvius recorded some observational guidance (use volcanic ash from specific regions, immerse in seawater to cure), but the reasoning behind those observations — why that ash, what happens at the molecular level, what alternatives were tried and rejected — was never captured. The artifact outlasted the understanding by roughly a millennium.

## Engineering Translation

This is a stewardship failure. The Roman engineers who developed marine concrete held knowledge in trust. They transmitted the procedural knowledge (mix proportions, material selection) but not the reasoning (why pozzolana, what alternatives were considered, what constraints drove the selection). When the procedural knowledge was lost, the reasoning could not be reconstructed — there was no context record from which to inherit. The thread broke not because the knowledge was unavailable, but because the context that gave the knowledge its engineering meaning was never preserved. Vitruvius' *De Architectura* came closest to a context record, but it transmitted prescriptions rather than principles — it told future builders what to do, not why doing it worked or what failure modes to watch for. A steward transmits not just the decision but the landscape of reasoning that produced it (OE-0009). The Romans transmitted the decision (use pozzolana) without the landscape.

## The Stewardship Gap

Compare to the Antikythera example (thread integrity failure through total loss). Roman concrete represents a different and in some ways more insidious failure mode: the artifact survived, the material was visible and touchable, and the structures themselves stood as undeniable evidence that the material worked. But the reasoning behind it was inaccessible. Medieval builders who harvested Roman concrete as rubble did not lack access to the artifact — they were literally standing on it. What they lacked was the engineering context: why this particular mixture, bound by this particular chemistry, behaved the way it did. A steward who transmits only the artifact without its engineering context transmits the shell, not the substance. The modern recovery of Roman concrete chemistry (Jackson et al., 2017, *American Mineralogist*) required 200 years of materials science that the Romans' reasoning could have provided directly, had it been preserved as a context record rather than a collection of empirical prescriptions. The cost of the stewardship gap was not the loss of the artifact (it survived) but the loss of the reasoning that would have accelerated its re-discovery by centuries.

## Modern Stewardship Implication

When an engineer documents only the final design — the mix proportions, the specification, the drawing — but not the reasoning, alternatives, constraints, and verification that produced it, they commit the same stewardship failure as the Roman concrete builders. The artifact is preserved; the understanding is not. A modern structural engineer who specifies a concrete mix design without recording why this particular mix was chosen over alternatives, what performance trade-offs were evaluated, what environmental conditions it was optimized for, and what failure modes were considered, is producing a 21st-century Vitruvius — a document that tells the next engineer what to do but not why. When conditions change (new aggregate sources, different environmental exposures, updated performance requirements), the next engineer cannot adapt the specification because they do not understand the reasoning behind it. The steward's obligation is not merely to preserve the output but to preserve the reasoning that makes the output interpretable and extensible by the next practitioner (OE-0009).

## Sources

Jackson, M. D., Mulcahy, S. R., Chen, H., Li, Y., Li, Q., Cappelletti, P., & Wenk, H.-R. (2017). "Phillipsite and Al-tobermorite mineral cements produced through low-temperature water-rock reactions in Roman marine concrete." *American Mineralogist*, 102(7), 1435-1450. Oleson, J. P., Brandon, C., Cramer, S. M., Cucitore, R., Gotti, E., & Hohlfelder, R. L. (2014). "The ROMACONS Project: A Contribution to the Historical and Engineering Analysis of Hydraulic Concrete in Roman Seaports." *International Journal of Nautical Archaeology*, 43(1), 134-157. Vitruvius. *De Architectura*, Book II, Chapter 6.

## Self-Fading Assessment

This example builds a bridge from the abstract concept of "stewardship" to a concrete historical case where transmitting the artifact without transmitting the reasoning produced a millennium-long gap in engineering understanding. The reader has crossed the bridge when they recognize that the difference between a specification and a context record is the difference between Vitruvius' prescriptions and what a full stewardship record would have provided — and when they can identify the same pattern in their own documentation practices. Once that recognition is stable, the Roman concrete example has served its purpose and can be set aside.