The road, Wales Coast Path and Ffestiniog Railway cross Traeth Mawr on an embankment known as the Cob. Traeth Mawr means 'Large Beach' and is named in the ancient Mabinogi legends (see below).
The Cob was completed in 1811 after four years of construction. The drawing, courtesy of the National Library of Wales, shows it taking shape in 1810.
The embankment was part of a grand plan by William Alexander Madocks, a wealthy MP who had acquired various bits of land in the area. Its construction was challenging and depended on the skills of John Williams, the agent for the MP’s Welsh estate who was based at Ynys Tywyn during the project.
The embankment and associated facilities for control of water allowed a large area of land to be drained and used for agriculture. The sea broke through during a storm in 1812. Almost 900 men from across North Wales, with more than 700 horses, offered their labour and the gap was eventually closed.
Madocks also had an eye on proposals to develop Porthdinllaen harbour, on the Llŷn Peninsula, as the main port for ships to Dublin. Road improvements would be needed, and Madocks hoped the route would involve his new embankment. However, Holyhead was developed instead of Porthdinllaen, and the improved road passed through Snowdonia far to the north of Traeth Mawr.
The diverted Afon Glaslyn scoured a deep new channel where William had a new harbour built in the 1820s – the basis of the new town of Porthmadog. He died in 1828, before construction of the Ffestiniog Railway brought large volumes of Blaenau Ffestiniog slates to the harbour, using the Cob for the final 1.5km of the journey. Narrow-gauge trains still cross the Cob, now carrying sightseers rather than slates.
The opening of the Porthmadog bypass road in 2011 relieved the Cob of through traffic and summer-holiday tailbacks. The 1890s photo on the right shows part of the view inland from the Cob – click here for our page about the mountains’ names.
According to The Mabinogi, Traeth Mawr is where two warring sides agreed to settle their conflict by a duel between Pryderi, from South Wales, and Gwydion from the North. Gwydion had triggered the conflict by stealing Pryderi’s pigs. With the help of his magical powers, he won the duel near Maentwrog, where Pryderi was buried.