Complex sentence: The blaze was caused by sparks from an open fire in St. Mary's Street near Northampton Castle, and devastated the town centre, destroying about 700 buildings (out of 850) including All Saints church, in six hours.
Split into simpler sentences: The blaze was caused by sparks from an open fire in St. Mary's Street, near Northampton Castle. The fire devastated the town centre, destroying about 700 buildings (out of 850) including All Saints church, in six hours.