The inner pier at Port St Mary was completed in 1812; it is one of the oldest surviving harbour structures on the Island.


The dogleg structure extends out a total of 225m to the Bealevayer Rock, protecting the harbour from the south-east and east.  Its end is marked by a lighthouse (3898.00).


The inner harbour, which is tidal, was improved by the creation of the new west quay in 1848 and the port's facilities were later significantly enlarged by the completion of the outer breakwater in 1886 (further extended in 1892), creating the outer harbour which is accessible at all states of the tide.