There are several theories concerning the origins of Gregorian and Old Roman chants, but one prominent hypothesis, supported by Apel and Snow, posits that both chant traditions derive from a common Roman ancestor in use circa 750 AD. In order to consolidate ecclesiastical power and strengthen their political ties to the power of the Roman church, the Franks, especially under the Carolingian rulers Pepin and Charlemagne, brought this older Roman chant north. There it was subsequently modified, influenced by local styles and Gallican chant, and categorized into the system of eight modes. This Carolingian, or Frankish-Roman, chant, became known as "Gregorian." In the meantime, the local chant remaining in Rome gradually evolved into the form in which it was eventually notated, at the same time that Gregorian was supplanting it in Rome.