In Latin with a parallel English translation. The Gaii Institutionum Juris Civilis Commentarii Quatuor, or Institutes of Gaius, was compiled around 161 CE. It is a deeply influential elementary textbook on Roman private law. Well-arranged and clearly written, it was the standard textbook for the next 300 years. One of the five authorities accepted by Justinian, it is the primary source of the Institutes. It was also the basis of the Breviarium Alaricianum, or Lex Romana Visigothorum. Gaius [c.115-180] was a teacher and writer who probably lived in Rome. The Tituli ex Corpore Ulpiani, also known as the Epitome Ulpiani, Regulae Ulpiani or Rules of Ulpian is a collection of legal rules attributed to Ulpian [c.160-228 CE], who is considered to be the last great classical Roman jurist. Many of the rules in this collection are similar to those in Gaius, and it is fruitful to have both works in the same volume for the purposes of comparison and clarification.