The village was traditionally founded by the 6th-century CornishSaint Cybi. According to legend, he is supposed to have crossed the Bristol Channel with ten followers. The life of St. Cybi, written much later and therefore including some questionable material, records that the local king, Edelig son of Glywys, threatened to evict them from his land, but as he approached them he fell from his horse, which died, and he and his men became blind. Edelig then prostrated himself and gave his body and soul to God, and he and his attendants were immediately cured and the horse restored to life. Edelig then, in thanks, gave Cybi land for two churches, including the one which became known as Llangybi, and another at an unspecified location where he is reported to have left a handbell.
Church of St. Cybi
The existing church, dedicated to St. Cybi, has been described as "one of the most interesting in the Usk valley" and "a delight". The tower, nave and chancel all date from the 13th or 14th century, and the church has 17th-century internal fittings, including the pulpit, font, and monuments to the local Williams family. There are also wall paintings dating from the late medieval period and the 17th century. One which is of particular interest is a "Christ of the trades", or more correctly a Sunday Christ, of which there are very few in the UK. Outside is the site of a traditional well, also named for St. Cybi. The church is a Grade II* listed building. The church is in regular use and is now part of a benefice with Llanbadoc, Tredunnock and Coed-y-paen. There is a bell ringing club. In 2015 the church was temporarily closed after major problems were discovered with the walls. Professional inspections revealed that the ceiling was at risk and several rare 15th and 17th century paintings were in danger of falling off the walls from hidden damp. With the estimated cost of renovation work put at possibly £100,000, a local fund-raising campaign was established to save the church. With the help of various funds, such as the Heritage Lottery Fund, work began. In October 2015 Monmouth MP David Davies boosted the appeal by giving Reverend Pamela Love, assistant curate for the four churches in the Llangybi group, two open return first class train tickets. Regular services continue to be held in the chancel.
Llangibby or Tregrug Castle
The site of Llangibby Castle, also known as Tregrug Castle, is located almost a mile outside the village. The estate, including an existing motte and bailey castle, came into the ownership of the de Clare family in 1245. A new large, ambitious and heavily fortified stone castle was started in the early 14th century possibly by Bogo de Clare, uncle of Gilbert de Clare who was killed at Bannockburn in 1314. For a while it was within the dispensation of the Despenser family and it may have been Hugh Despenser the Younger who began to build what remains of the late medieval construction. It was attacked during the revolt of Llywelyn Bren in 1316. After coming into Crown ownership it was sold to the Williams family of Usk in 1554. During the English Civil War the run-down castle was re-fortified and held by Sir Trevor Williams, 1st Baronet, an influential local man whose loyalties to his locality, community and family remained firm even though his loyalties to his King, patrons and the establishment were severely tested by events during that turbulent time. The castle was slighted as a result. Its ruins still remain, surrounded by dense woodland. They include a huge rectangular walled enclosure on the top of the hillside, surrounded by ditches, and including the remains of a large stone tower, known as the Lord's Tower, and a gatehouse. The Williams family built a new house nearby later in the 17th century; it was demolished in 1951. In 2010, the old castle remains at Tregrug were investigated by the Channel 4 series Time Team. The programme concluded that the ditches surrounding the walls were Civil War defences, and that the castle had been substantially remodelled in the 17th century to provide a new main entrance and to landscape the area inside the walls to form a "pleasance" containing gardens and fountains.
The White Hart inn a Grade II* listed building, was first built in the early 16th century and was to become the property of Henry VIII as part of Jane Seymour's wedding dowry. A century later Oliver Cromwell is reputed to have used it as his headquarters in Monmouthshire during the English Civil War. The interior still retains no fewer than 11 fireplaces from the 17th century, a wealth of exposed beams, original Tudor period plasterwork and even a priest hole. The Catholic martyr David Lewis preached in the inn when the church was closed to him; he was executed in Usk in 1679. In 2003 Philip Edwards, former King Alfred professor of English literature at Liverpool University suggested that T. S. Eliot made cryptic reference to this pub and the village well in his 1935 poem "Usk". Refurbishment of the inn was completed in April 2007.
Multiple family murder
In 1878 Spanish sailor Josef Garcia was convicted, at the Sessions House, Usk, of the murder in the village of William and Elizabeth Watkins and their three youngest children.
Governance
Llangybi is included in the Llangybi Fawr electoral ward, which stretches northeast-southwest from Llantrisant to Llanhennock. The total population of this ward at the 2011 census was 1,861.
