Eastern Main Lines Alnmouth to Berwick including the Seahouses and Tweed Dock branchesEastern Main Lines Alnmouth to Berwick including the Seahouses and Tweed Dock branches In 1850 the completion of the Royal Border Bridge, linking the two banks of the River Tweed, was the final piece of the jigsaw that saw the East Coast Main Line link London with Edinburgh. The line covers several intermediate stations that were closed during the 1950s. The Seahouses and Tweed Dock branches provide interesting studies of lines serving East Coast