The Libri Feudorum is a twelfth century collection, originating in Lombardy

Lombardy

Lombardy is one of the 20 regions of Italy. The capital is Milan. One-sixth of Italy's population lives in Lombardy and about one fifth of Italy's GDP is produced in this region, making it the most populous and richest region in the country and one of the richest in the whole of Europe...

, of feudal customs. The work gained wide acceptance as a statement of the various rules governing the relation of lord and vassal.
Later in the century it was integrated into civil law

Civil law (legal system)

Civil law is a legal system inspired by Roman law and whose primary feature is that laws are codified into collections, as compared to common law systems that gives great precedential weight to common law on the principle that it is unfair to treat similar facts differently on different...

. It is a significant example of an increasing need for the rationalization of law.

Its integration by civilians into the larger corpus of civil law demonstrates the interaction of Roman law

Roman law

Roman law is the legal system of ancient Rome, and the legal developments which occurred before the 7th century AD — when the Roman–Byzantine state adopted Greek as the language of government. The development of Roman law comprises more than a thousand years of jurisprudence — from the Twelve...

concepts with local law.
J. G. A. Pocock noted that "Lombard feudalism possessed, in the Libri Feodorum, the only written systematization of feudal law that had become part of the general legal heritage of Europe."