The Swellies (Pwll Ceris), lying within Nelson’s gaze between the Britannia and Menai Suspension Bridges, is a choke point where strong tides of 5-8kts run, making it a significant navigational obstacle, particularly in the days of sail. This rock-strewn reach, eight cables long, was formed by fault line activity, glaciation and rising sea levels, which, about 5,000 years ago, finally inundated the strait, separating Anglesey from mainland Wales.
In 1693, Captain Grenvile Collins wrote in his Coasting Pilot “...the rocks at the Swilly are dangerous, the passage narrow, and the tydes very strong; and be sure to pass the Swilly at a slack tyde.”
Building the Telford’s Menai Suspension Bridge and Stephenson’s Britannia Bridge across the strait replaced the passenger ferry, the fording of cattle across the strait and provided…