Complex sentence: His first known commission was for the design of Montacute House in c1598, this is one of the finest Elizabethan mansions in the country, it was designed for Sir Edward Phelips.
Split into simpler sentences: His first known commission was for the design of Montacute House in c1598. This is one of the finest Elizabethan mansions in the country and was designed for Sir Edward Phelips.