Complex sentence: The presence of Jews in Cologne was documented in AD 321; when exactly the first Jews arrived in the Rhineland area cannot now be established, but the Cologne community claims to be the oldest north of the Alps.
Split into simpler sentences: The presence of Jews in Cologne was documented in AD 321. When exactly the first Jews arrived in the Rhineland area cannot now be established, but the Cologne community claims to be the oldest north of the Alps.