Some articles on tetrarchic:

Tetrarchy - Regions and Capitals
... These centres are known as the Tetrarchic capitals ... The four Tetrarchic capitals were Nicomedia in northwestern Asia Minor (modern Izmit in Turkey), a base for defence against invasion from the Balkans and Persia's ... years later and from uncertain sources), misunderstood the Tetrarchic system in this respect, believing it to have involved a stricter division of territories between the four emperors ...