Complex sentence: During the 18th century the navigation was improved by longer cuts to bypass difficult or circuitous stretches of river, but the major improvements were made in the last quarter of the century by civil engineers John Smeaton and William Jessop.
Split into simpler sentences: During the 18th century the navigation was improved by longer cuts to bypass difficult or circuitous stretches of river. The major improvements were made in the last quarter of the century by civil engineers John Smeaton and William Jessop.