Complex sentence: By order of the city council, the ground floor was in 1348 rebuilt with stone walls--until 1401, the Zurich council used it as city hall--and sold to a group of nobles and wealthy merchants, belonging to the Constaffel.
Split into simpler sentences: By order of the city council, the ground floor was rebuilt in 1348 with stone walls for use as the city hall. In 1401 the building was sold to a group of nobles and wealthy merchants belonging to the Constaffel.