The village of Trefechan is within the parish of Vaynor.

Prior to the industrial revolution, Vaynor would have been an agricultural parish, with the only links to industry being small flour or fulling mills (cloth) and some small scale quarrying.
Arable farming was practised from around 3000 BC in Vaynor. Many burial Cairns have been discovered in the area and a bronze dagger excavated on Cilsanws Mountain is the oldest manmade metal object to be found in Merthyr Tydfil.

Morlais Castle

Overlooking Trefechan are the remains of Morlais Castle.
Gilbert de Clare, Lord of Glamorgan built Morlais Castle around 1288 AD. By this time Gilbert had already built Caerphilly Castle.
Humphrey de Bohun, Lord of Brecknock disputed de Clare's claim on the land Morlais Castle was built. This dispute culminated in 1291 with the Battle of Maesvaynor.

The battle is remembered in an old Welsh poem:

'The battle was won by the men of Bohun,
And blood like an ocean in Vaynor was seen.'
During the Welsh Rebellion of the thirteenth-century Morlais Castle was briefly held by Welsh rebels and used as a stronghold in the battle for Welsh independence.
After Edward I won his war against the Welsh he destroyed parts of Morlais Castle to prevent it from ever being used as a stronghold again.
Vaynor remained an agricultural parish until the Industrial Revolution began in the late 18th century. At this time the area changed dramatically. Houses were hastily built for workers, woodland was removed for fuel and huge limestone quarries were created.

Limestone Quarrying

There are many Limestone Quarries in the Vaynor area and their remains are still visible along the trails and on the hillsides.
Limestone was used in the ironworks to purify the iron-ore.
Vaynor Quarry is the closest quarry to Trefechan. Created by the Crawshay family Vaynor Quarry was in use right through to the twentieth-century. In 1957 the quarry produced 1000 tons of limestone per day. Eventually production stopped in the 1990's.

Vaynor House

On the land where the Trefechan Estate now stands stood another of the Crawshay homes, Vaynor House.
Built in the 1860's Vaynor House was a sizeable house with three reception rooms, nine bedrooms, domestic offices, stables and cowsheds, all of which was surrounded by 15.5 acres of pasture land.
Vaynor House was demolished around 1947 when the housing estate of Trefechan was constructed.