The river has 22 road crossings, including some medieval stone bridges. The oldest bridge still extant is at Horsebridge (1437), and the next oldest is Greystone Bridge near Lawhitton — this arched stone bridge was built in 1439. Gunnislake New Bridge was built in 1520 by Sir Piers Edgcumbe, the owner of Cotehele and Mount Edgcumbe. The Gunnislake bridge was a main route into south east Cornwall and the lowest bridge over the Tamar until the Tamar Bridge at Saltash was opened in 1962. The lower Tamar is spanned also by the Royal Albert Bridge (built 1859), a rail bridge now adjacent to the newer Tamar Bridge. Both of these bridges are between Saltash (known as the 'Gateway to Cornwall') and Plymouth. Further downstream, crossing the Hamoaze, is the Torpoint Ferry — a chain ferry connecting Torpoint to Devonport — and at the most downstream part of the Hamoaze there is also the Cremyll Ferry. The Calstock Viaduct is another notable structure on the Tamar, being 120 feet (37 m) high with twelve 60-foot (18 m) wide arches, of which three of the piers stand in the river, and was built between 1904 and 1907. Listed below are all crossings of the River Tamar, in order heading downstream. All cross the county boundary between Devon and Cornwall, except for four that are noted. The total length of the tidal river (which, like other tidal waters in England, has public right of navigation) is . The normal tidal limit (noted on Ordnance Survey maps as 'NTL') is a weir just downstream of the village of Gunnislake. Waterborne traffic through the Hamoaze is controlled by the Queen's Harbour Master for Plymouth, who is responsible for managing navigation along the entire tidal Tamar. The Royal Navy has one of its three main naval bases at Devonport, situated on the Hamoaze, upstream of which the river is now used largely by recreational craft. Excursions operate (April to October only) on the river between Plymouth and Calstock; excursions used to operate as far as Morwellham Quay, but were suspended indefinitely in 2016. A passenger ferry also operates April to October between Cotehele Quay and Calstock. A typical Tamar vessel was a sailing barge, built on the open river bank, of up to 60 tons, with a peaked, gaff-rigged mainsail and a fore staysail.