Complex sentence: It was the third oldest metropolis in the region of Bythinia, in northwestern Asia Minor, after Nicea and Nicomedia, while its prelate officially styled as "Exarch of all Bithynia".
Split into simpler sentences: It was the third oldest metropolis in the region of Bythinia, in northwestern Asia Minor, after Nicea and Nicomedia. Its prelate styled as "Exarch of all Bithynia".