Complex sentence: This fair is known to have been held on 23 June each year, but it seems likely that the earlier fairs were held on the same day, which is the feast day of St Ætheldreda, long associated with the site.
Split into simpler sentences: This fair is known to have been held on 23 June each year. But it seems likely that the earlier fairs were held on the same day, which is the feast day of St. Æthelreda, long associated with the site.