Llandeilo, United Kingdom

The early Christian settlement that developed around the Saint Teilo's Church prospered, and by the early 9th century it had attained considerable ecclesiastical status as the seat of a Bishop-Abbot. The Church of St Teilo soon became a "mother church" to the surrounding district, acquiring an extensive estate, and possessing one of Wales' most beautiful and finely illustrated manuscripts – the Gospel Book of Saint Teilo. The discovery of fragments of two large Celtic crosses from this period provides further testimony to Llandeilo's importance and prestige as an early ecclesiastical centre. Towards the end of the 9th century, the importance of Llandeilo as a spiritual centre had started to decline.

Dinefwr Castle (anglicised as Dynevor) overlooks the River Tywi near the town. It lies on a ridge on the northern bank of the Tywi, with a steep drop of about 250 feet (76 m) to the river. Dinefwr was the chief seat of the kingdom of Deheubarth.

The estate of Golden Grove lies near the town, and further away, the impressive Carreg Cennen Castle, another Welsh stronghold. The remains of Talley Abbey can be seen 6 miles (9.7 km) away to the north of the town. 10 miles (16 km) further north are the remains of the Roman Dolaucothi Gold Mines.

In the centuries that followed the Norman conquest of England, the Bishop of Llandaff and Bishop of St David's both claimed Llandeilo for their respective dioceses. By the early 12th century, Llandeilo came under the patronage of the Bishopric of St David's, an ecclesiastic borough that became responsible for the affairs of the town including its development as an important medieval market centre to an extensive agricultural hinterland. Until the middle of the 20th century, a fair called St. Teilo's Fair, which had been authorised initially by Edward I of England in 1291, was held annually in the churchyard. Some of the agricultural produce and other goods offered for sale are recorded to have been displayed on the tombstones.

The town was put to the torch during Owain Glyndŵr's march through the Tywi Valley in July 1403. Nearby Carreg Cennen Castle was besieged by Yorkist forces in 1461 during the Wars of the Roses and partially demolished.

At the Reformation, the town was at the centre of the parish known as Llandeilo Fawr. It was in the Diocese of St Davids and part of the archdeaconry of Carmarthen. In 1560, the bishop of St Davids recorded the population of Llandeilo Fawr as 620 households (perhaps amounting to 2,790 people), many of whom would have lived in Llandeilo itself.

In the middle of the 17th century, Llandeilo was in the area of influence of the royalist general Sir Henry Vaughan. A royalist skirmish took place in the town in April 1648, defeating elements of the New Model Army.

In 1887, John Bartholomew's Gazetteer of the British Isles described Llandeilo as having a population of 1,533. He observed that “the principal trade of the town is in corn and flour; the other industries include woollen cloth mills, timber and saw mills, and tanneries”.