Justinian's code was created by Emperor Justinian during his reign of the Byzantine Empire. The reason why this code was created was to take all of the different Roman laws and put them into one single place. This code became a set of laws that other empires/countries would follow for centuries.
This code was significant because it dealt with several different elements of society including criminal justice (punishing criminals), marriage, property rights, slavery, and women's rights. This unified set of laws ended up being used as the basis for law in the former Byzantine Empire for roughly 900 years.