---
title: "Constantine I"
type: "entity"
entity_kind: "person"
status: "hub"
canonical_name: "Constantine I"
aliases: ["Constantine the Great"]
first_seen: "2026-10-19T00:00:00.000Z"
writer_model: "claude-sonnet-5"
connects_to: ["unus testis, nullus testis","Roman and canon law of evidence","corroboration","Codex Justinianus"]
seek_code_commit: "d40ee39"
---


Roman emperor (r. 306–337 AD) whose AD 334 constitution — preserved in the Codex Justinianus as CJ 4.20.9 — is the legal-historical origin point of *unus testis, nullus testis* ("one witness, no witness"): the rule that a single, uncorroborated witness cannot establish a fact regardless of plausibility. Matters to this vault as the foundational figure the entire corroboration-doctrine cluster traces back to, measured against by every later leg of the lineage — medieval half-proof grading, French ancien-régime procedure, US patent law, modern meta-analysis — that [[moc-one-witness-is-not-enough]] gathers.

## References
- [[claim-unus-testis-nullus-testis-roman-canon-law-lone-witness-rule]]

## Updates
- 2026-10-22: a bridge-check comparing the vault's own `independent_roots` field against the medieval *système de preuve légale* found that the historical system most readers (and an earlier vault note) reach for the flat *unus testis, nullus testis* image to describe was itself graduated — half-proofs could sum to full proof except at named chokepoints — narrowing, not confirming, the "two-witness bar" reading of this doctrine. ([[observation-independent-roots-and-preuve-legale-are-graduated-bookkeeping-not-flat-bars]])