An oval barrow is the name given by archaeologists to a type of prehistoric burial tumulus

Tumulus

A tumulus is a mound of earth and stones raised over a grave or graves. Tumuli are also known as barrows, burial mounds, Hügelgrab or kurgans, and can be found throughout much of the world. A tumulus composed largely or entirely of stones is usually referred to as a cairn...

 of roughly oval shape.

In the British mid to late Neolithic

Neolithic

The Neolithic Age, Era, or Period, or New Stone Age, was a period in the development of human technology, beginning about 9500 BC in some parts of the Middle East, and later in other parts of the world. It is traditionally considered as the last part of the Stone Age...

 and early Bronze Age

Bronze Age

The Bronze Age is a period characterized by the use of copper and its alloy bronze as the chief hard materials in the manufacture of some implements and weapons. Chronologically, it stands between the Stone Age and Iron Age...

, oval barrows may indicate a transition between earlier long barrow

Long barrow

A long barrow is a prehistoric monument dating to the early Neolithic period. They are rectangular or trapezoidal tumuli or earth mounds traditionally interpreted as collective tombs...

s with multiple burials and the later, more individual round barrow

Round barrow

Round barrows are one of the most common types of archaeological monuments. Although concentrated in Europe they are found in many parts of the world because of their simple construction and universal purpose....

s.

Judging from those sited in or near the Thames Valley, there is much doubt as to how oval barrows are related to the burials found within them and funerary practices, because there can be a long gap of many years between an original burial and the construction of the barrow.

Whiteleaf Hill

There is a neolithic oval barrow near the top of Whiteleaf Hill, Monks Risborough, Buckinghamshire (National Grid: SP 822040), which was first excavated by Sir Lindsay Scott between 1934 and 1939 and re-excavated from 2002 to 2006 by Oxford Archaeology (assisted by the Princes Risborough Countryside Group). The mound is roughly oval, but indented on the north-eastern side, making it somewhat kidney-shaped. The barrow held only one burial and radio-carbon dating has shown that the death, the burial and the building of the mound probably all took place within the period 3,750-3,100 B.C., but at different times within that period. The remains appeared to have been placed between two large vertical posts, 1.2 metres apart. Pottery shards and animal bones were found at the core of the mound and the excavators suggest that these came from ceremonial feasting when the mound was built.

Dorney Reach

This is a mid-neolithic barrow dated to the approximate period 3300-2800 BC. Previously known only from a cropmark, magnetometry and resistivity surveys have produced more detailed information about this unexcavated site, which is on level ground on the flood plain of the River Thames at SU 9170 7935, 250 metres from the river. They reveal an oval ditch with external dimensions of about 20 by 12.5 metres. The axis lies NNE-SSW. Indications of two pits at the centre may represent a split-timber mortuary structure, as was found at Whiteleaf.

Marsh Lane East (site 2)

It is believed that this was originally a neolithic oval barrow, but it was re-cut in the Bronze Age, so that little of the original barrow remains.