A modern law student is told that one medieval collection organised the whole body of Roman law and shaped later European legal thinking. Which collection is meant?

Explanation

The collection gathered centuries of scattered Roman legal material into one ordered body, and when it was studied again in later medieval Italy it became the foundation of legal teaching across much of Europe. A Frankish royal code is the tempting wrong turn here, because rulers did issue written law, but Frankish law was local and customary and it neither organised Roman law nor shaped later legal study.