Complex sentence: He was the chief promoter of the construction of the first dry dock (1708) and steered a bill through Parliament to authorise it, and the building of St Peter's and St George's churches were due in great measure to his efforts.
Split into simpler sentences: He was the chief promoter of the construction of the first dry dock in 1708 and steered a bill through Parliament to authorise it. In addition, the building of St Peter's and St George's churches were due in great measure to his efforts.