In 2016, on land owned by the Sylva Foundation, an Anglo-Saxon building was excavated by Oxford University School of Archaeology. This early habitation was first revealed in the 1890s, in the first ever use of cropmarks to discern archaeological remains. There is also evidence of a possible Frankish settlement: a 5th-century grave that contained high-status Frankish objects. Later settlement evidence is more extensive: Iron Age and Roman presence is indicated by trackways, various buildings (enclosures, farms and villas), burials (cremation and inhumation), and pottery and coins. Bronze Age double-ditch enclosures and middle Bronze Age pottery were identified in the 1960s, and early Bronze Age items, such as an axe and spearhead, have been found in the Thames. The village is supposedly named after a Saxon chieftain, named Witta, but there is evidence of an earlier settlement.

To the south-east are neighbouring Little Wittenham which has a much smaller population but a much larger area and within this parish is Wittenham Clumps, also called the Sinodun Hills. About 1 mile (1.6 km) to the east, across the river, is the Roman town of Dorcic – now Dorchester-on-Thames. The river navigation follows Clifton cut, not the meander. The village is on the outside of a meander in the River Thames, on slightly higher ground than the flood plain around it. It was part of Berkshire until the 1974 boundary changes transferred it from Berkshire to Oxfordshire, and from the former Wallingford Rural District to the new district of South Oxfordshire. Long Wittenham is a village and small civil parish about 3 miles (5 km) north of Didcot, and 3.5 miles (5.6 km) southeast of Abingdon.

Hewitt berkshire edge