Rhosydd quarry was a slate quarry in the Moelwyn mountains, northeast of Porthmadog in North Wales. Small-scale working of the site began in the 1830s, but was hampered by the remote location, and the lack of a transport system to carry the slates to markets. The Rhosydd Slate Company was formed in 1853, and became a limited company in 1856. Transport was made more difficult by the attitude of the Cwmorthin quarry, through whose land the most obvious route to the Ffestiniog Railway ran. A solution was found in 1864, with the opening of the Croesor Tramway, to which the quarry was connected by one of the longest single-pitch cable-hauled inclines in Wales. Huge amounts of money were spent on development work, and the company, unable to make adequate returns, went into voluntary liquidation