Final answer:
The Romans spread legal principles through the tradition of using precedent, the concept of innocence until proven guilty, codifying laws in the Twelve Tables, and extending Roman law to citizens in provinces.
Step-by-step explanation:
The Romans spread legal principles through various means. They initiated the tradition of using precedent to shape legal decisions and introduced the idea that there is a spirit to laws that is sometimes more important than a literal interpretation. Additionally, the Romans established the concept of someone being innocent until proven guilty, which was a radical idea at the time.
Rome codified their laws in the Twelve Tables, which were publicly available and reduced the chances of corruption. They also developed the Law of Nations, an early form of international law.
Roman law extended to Roman citizens even in provinces far from Rome, and this was further expanded when Emperor Caracalla extended citizenship to all free men and women in the empire.