Saint Constantine developed the main administrative divisions of what?
Theme (Byzantine district) The themes or themata (Greek: θέματα ; singular θέμα, "thema") were the main administrative divisions of the middle Eastern Roman Empire. They were established in the mid-7th century in the aftermath of the Slavic invasion of the Balkans and Muslim conquests of parts of Byzantine territory, and replaced the earlier provincial system established by Diocletian and Constantine the Great. In their origin, the first themes were created from the areas of encampment of the field armies of the East Roman army, and their names corresponded to the military units that had existed in those areas. The theme system reached its apogee in the 9th and 10th centuries, as older themes were split up and the conquest of territory resulted in the creation of new ones. The original theme system underwent significant changes in the 11th and 12th centuries, but the term remained in use as a provincial and financial circumscription until the very end of the Empire.
Maxima Caesariensis Maxima Caesariensis (Latin for "The Caesarian province of Maximus"), also known as Britannia Maxima, was one of the provinces of the Diocese of "the Britains" created during the Diocletian Reforms at the end of the 3rd century. It was probably created after the defeat of the usurper Allectus by Constantius Chlorus in  296 and was mentioned in the c. 312 Verona List of the Roman provinces. Its position and capital remain uncertain, although it was probably adjacent to Flavia Caesariensis. On the basis of its governor's eventual consular rank, it is now usually considered to have consisted of Augusta or Londinium (London) and southeastern England.