Short answers, pulled from the story.
Priests served as the initial heads of the judicial system during the archaic Roman period between 650 and 264 BC. They examined applicable rules in the first phase of a trial known as In Iure before the case moved to ordinary citizens in the second phase. This early system relied on social norms called Mos Maiorum rather than codified statutes until the Twelve Tables were written between 451 and 449 BC.
Praetors replaced priests as the heads of the judicial system during the pre-classical Roman era between 264 and 27 BC. These elected officials issued edicts that created a body of law known as praetorian law to supplement the rigid Mos Maiorum. The process eventually evolved into a single phase called cognitio extraordinaria under Emperor Hadrian where professional judges heard cases.
The Corpus Iuris Civilis contains four distinct parts created during the post-classical era from 284 to 565 AD. These parts include the Institutiones as an introduction, the Digesta or Pandectae as a collection of edicts, the Codex containing all imperial laws, and the Novellae holding new laws. The rediscovery of the Digesta in 1070 sparked a revival of legal education in the Middle Ages.
The common law system allows courts to interpret constitutions and statutes while making law based on prior case law through the principle of stare decisis. In contrast, lawmakers in France prohibited judges from interpreting the law and reserved that power solely for the legislature during the civil law tradition. The common law system relies on an adversarial process where parties find evidence while the civil law often uses an inquisitorial process where judges investigate evidence.
In the United States federal court system justices are appointed by the President and approved by the Senate to serve for life terms. Japan requires assistant judges to serve five years before qualifying to sit alone and requires ten years of experience for judges. The Mexican Supreme Court features eleven ministers appointed by the President and approved by the Senate to serve fifteen-year terms while other justices are appointed by the Supreme Court for six-year terms.