In 1942/43, the most significant find of La Tène period artefacts in the British Isles was found here during the construction of a Royal Air Force base.

The first object found was a 3m long iron chain used for slaves. It was not initially recognised as antique. It was attached to a tractor and was used to pull trucks out of the mud. Despite its age, the chain served this function well. A total of 181 artefacts made of iron, copper and bronze were found, mainly various weapons, around 22 fittings and remains of chariots, horse harnesses, cauldron fragments, fittings for cult staffs and sceptres. A moon-shaped, gold-plated bronze plate from the 2nd or 1st century BC is divided into triskels by circular strokes. The deliberate bending and breaking of the artefacts revealed their purpose as sacrificial offerings.

The period of use as a sacrificial site was dated from the 2nd century BC to the Roman invasion (1st century AD), with most of the offerings being deposited between 150 BC and 60 AD.

When the Roman general Gaius Suetonius Paulinus conquered Anglesey around 60 AD, the island was an important centre of Druidism, which confirms the significance of the sacrificial site. From this time onwards, sacrifices probably no longer took place in Llyn Cerrig Bach.