A church has been located on the site of current St Tewdric's Church since the 6th century. Following the Norman conquest of Wales, the Celtic foundation was rebuilt in the twelfth and thirteenth centuries, in the Early English style. The chancel and nave arcades of the existing church date from those periods, though the west pier of the north arcade dates from the previous century. It was later grandiosely enlarged by John Marshall, the Bishop of Llandaff between 1478 and 1496. Under his stewardship, the aisles were widened, a porch added on the south side, and the tower, built of ashlar blocks, was constructed.
According to the Liber Landavensis, when King Tewdrig fell in battle against the Anglo-Saxons at the River Wye, it was his desire to be buried on Ynys Echni; however the soldiers were unable to get his body there. Instead, he was buried at Mathern by his son Meurig ap Tewdrig. An oratory was built on top of his grave, and the land surrounding it was given to the Celtic Christian Bishops of Llandaff. Nearby Mathern Palace was later built for the use of the bishops.
A stone coffin, thought to contain the remains of Tewdrig, was first discovered when Francis Godwin was bishop in 1614; at that time it was moved to the chancel. An urn containing the heart of another bishop, Miles Salley, was unearthed and reburied at the same time.
In the 1880s, the Church of England ordered a renovation of the church. During the renovation, the stone coffin was rediscovered under the altar, with a skeleton with the skull split by an axe blow, in the same way that Tewdrig supposedly died. However historian Fred Hando claims from an eye-witness account that the skull only had a hole from a spear in it rather than an axe split. The remains were reinterred afterwards. On the wall of the chancel is a late 18th-century inscription noting that Tewdrig is interred in the church, with an addendum noting the rediscovery of the coffin in 1881.
Following restorations, the church now has no visible elements of the original Celtic church. The oldest parts of the church are the arcades of the nave and the arch over the chancel.
References:Monte d"Accoddi is a Neolithic archaeological site in northern Sardinia, located in the territory of Sassari. The site consists of a massive raised stone platform thought to have been an altar. It was constructed by the Ozieri culture or earlier, with the oldest parts dated to around 4,000–3,650 BC.
The site was discovered in 1954 in a field owned by the Segni family. No chambers or entrances to the mound have been found, leading to the presumption it was an altar, a temple or a step pyramid. It may have also served an observational function, as its square plan is coordinated with the cardinal points of the compass.
The initial Ozieri structure was abandoned or destroyed around 3000 BC, with traces of fire found in the archeological evidence. Around 2800 BC the remains of the original structure were completely covered with a layered mixture of earth and stone, and large blocks of limestone were then applied to establish a second platform, truncated by a step pyramid (36 m × 29 m, about 10 m in height), accessible by means of a second ramp, 42 m long, built over the older one. This second temple resembles contemporary Mesopotamian ziggurats, and is attributed to the Abealzu-Filigosa culture.
Archeological excavations from the chalcolithic Abealzu-Filigosa layers indicate the Monte d"Accoddi was used for animal sacrifice, with the remains of sheep, cattle, and swine recovered in near equal proportions. It is among the earliest known sacrificial sites in Western Europe.
The site appears to have been abandoned again around 1800 BC, at the onset of the Nuragic age.
The monument was partially reconstructed during the 1980s. It is open to the public and accessible by the old route of SS131 highway, near the hamlet of Ottava. It is 14,9 km from Sassari and 45 km from Alghero. There is no public transportation to the site. The opening times vary throughout the year.