How was the Justinian code one of Justinian's greatest accomplishments?

Nowadays Justinian's greatest achievement is considered the Corpus Juris Civilis, or Justinian Code (a compendium and revision of centuries or Roman law) because it has influenced the later development of civil law in Europe. However, we do not have any information about its impact at the time. In his days his reconquest of Italy, Tunisia and western Algeria, and southern Spain was probably considered his greatest achievement.