Twelve Tables

The Twelve Tables were the first written Laws of Rome compiled in 449 BCE under the Roman Republic (509-29 BCE). Prior to the 509 BCE, Roman Law was unwritten and based on a mix of Customary Law and Religion.
In 449 BCE, the Lex Duodecim Tabularum (Law of the Twelve Tables) was the Act that incorporated the Twelve Tables to be the basis of the Constitution of the Roman Republic.

It is generally considered that the Twelve Tablets are based on Greek Law, possibly derived from Magna Graecia, and partly on the Etruscan religion and its rituals.
In 451 BCE Livy recounts that ten Roman Citizens, the Decemvirii, were appointed to record the Roman Laws, and produced ten Tablets. The Plebians were unhappy with these Laws, and two more Tablets were added producing the Twelve Tablets.
In 449 BCE, the Lex Duodecim Tabularum (Law of the Twelve Tables) was the Act that incorporated the Twelve Tables to be the basis of the Constitution of the Roman Republic.
The Laws were written on twelve ivory tablets and displayed in the Forum Romanum. The originals were burnt when Brennius sacked Rome in 390 BCE, and copies reworked.
However, the Constitution was largely unwritten and so had no Codes. So, new Acts and Edicts were formulated on the basis of Precedent, ie, previous judgements of the courts.
The Twelve Tables stated the Rights and Duties of the Roman Citizen.
They formed the basis of Roman Law for the next one thousand years.

Under Hadrian (117-138 CE), the Twelve Tables and all previous Edicts and Decrees of the Roman Senate appear to have been collected into one Work called the Perpetual Edict in c.129 CE..
This was then used as a standard for Civil Jurisprudence.