Given the following context:

There have been railways in Portland since the early 19th century. The Merchant's Railway was the earliest—it opened in 1826 (one year after the Stockton and Darlington railway) and ran from the quarries at the north of Tophill to a pier at Castletown, from where the Portland stone was shipped around the country.  The Weymouth and Portland Railway was laid in 1865, and ran from a station in Melcombe Regis, across the Fleet and along the low isthmus behind Chesil Beach to a station at Victoria Square in Chiswell. At the end of the 19th century the line was extended to the top of the island as the Easton and Church Ope Railway, running through Castletown and ascending the cliffs at East Weares, to loop back north to a station in Easton. The line closed to passengers in 1952, and the final goods train (and two passenger 'specials') ran in April 1965.The Royal National Institution for the Preservation of Life from Shipwreck stationed a lifeboat at Portland in 1826, which was withdrawn in 1851. Coastal flooding has affected Portland's residents and transport for centuries—the only way off the island by land is along the causeway in the lee of Chesil Beach. At times of extreme floods (about every 10 years) this road link is cut by floods. The low-lying village of Chiswell used to flood on average every 5 years. Chesil Beach occasionally faces severe storms and massive waves, which have a fetch across the Atlantic Ocean. Following two severe flood events in the 1970s, Weymouth and Portland Borough Council and Wessex Water decided to investigate the structure of the beach, and coastal management schemes that could be built to protect Chiswell and the beach road. In the 1980s it was agreed that a scheme to protect against a one-in-five-year storm would be practicable; it would reduce flood depth and duration in more severe storms. Hard engineering techniques were employed in the scheme, including a gabion running 550 metres (600 yd) to the north of Chiswell, an extended sea wall in Chesil Cove, and a culvert running...

answer the following question:

Where was an extended sea wall built in the city where coastal flooding has affected residents for centuries? 

Chesil Cove