Complex sentence: An additional annual celebration, the Bartholomew Fair, was established in 1133 by the Augustinian friars and this over time became one of London's pre-eminent summer fairs, opening each year on 24 August.
Split into simpler sentences: An additional annual celebration, the Bartholomew Fair, was established in 1133 by the Augustinian friars. Over time, this became one of London's pre-eminent summer fairs, opening each year on 24 August.