If you enjoy public beaches, state parks or fishing piers, you can thank the sixth-century Roman emperor Justinian. He’s credited with introducing the public trust doctrine, a legal concept that forbids private ownership of certain natural resources, instead preserving them for public use. This idea has spread worldwide since then, protecting everything from beaches and streams to oyster beds and fish stocks.

It was an early tenet of English common law, later encoded in the Magna Carta, and also has a long history in U.S. courts, dating back to at least 1842’s Martin v. Waddell. During a 1983 case about water use at California’s Mono Lake, the U.S. Supreme Court specifically quoted this section of Roman law to explain public trust:

‘By the law of nature these things are common to mankind: the air, running water, the sea and consequently the shores of the sea.’
- Justinian Code of Rome, c. 534

The court ultimately added its own, slightly more specific wording:

‘[T]he public trust is more than an affirmation of state power to use public property for public purposes. It is an affirmation of the duty of the state to protect […]