Complex sentence: In 798, counties of Urgell, Osona, and Cerdanya were established under Borrell, and in 801, the greatest of the counties, Barcelona, was established under Bera.
Split into simpler sentences: In 798, Urgell, Osona, and Cerdanya were established under Borrell. In 801, the greatest of the counties, Barcelona, was established under Bera.