Complex sentence: Tomen yr Allt was the caput of the commote of Mechain Uwch Coed in the cantref of Mechain Mechain became part of the principality which became known later as Powys Wenwynwyn in 1160, when the Kingdom of Powys was divided.
Split into simpler sentences: Tomen yr Allt was the caput of the commote of Mechain Uwch Coed in the cantref of Mechain. In 1160, Mechain became part of the principality which later became known as Powys Wenwynwyn, when the Kingdom of Powys was divided.