More information : (SZ 00328603 - SZ 00488648) A feature which does not appear to be natural and which is known locally as an 'ancient causeway' is marked on the Pool Harbour Board's chart and recently on Admiralty Chart 2611 as running from Cleavel Point to Green Island with a long gap at South Deep. At a 'spring' low tide there is only 3ft of water over the feature and its silt. It has been known to harbour users as far back as the memory of the oldest fisherman who terms it the 'Roman Sunken Road'. (1-2)
Underwater and field investigation of the "causeway" in 1959 revealed that there was definitely firm material at a depth of 3ft and the width of the feature was indicated to be about 36ft with a rise at the centre of about 1ft. Several limestone flags were found lying on the flint and stones flint and stones and pieces of wood were also recorded, which had been bedded in the "causeway" underneath the limestone flags and lying side by side longitudinally; the condition of the wood was more in the keeping with a Medieval date rather than earlier. It was proved that there was a gap in the middle of the causeway but no collapsed central support for a bridge - Hutchins records that Green Island was once connected to the Ower peninsula by a bridge, the remains of which were visible in 1774. The purpose of the "causeway" is unknown but it may be Medieval although a Roman date cannot be entirely ruled out. Plan. (3).
RCHM record this feature under `Roman' and add that 'the causeway, undated, was probably surfaced with stone flags on a log courduroy laid axially." (4)
The Poole Harbour Heritage Project (from 1999) uncovered two stone structures. One was 160 metres long and 8-10 metres wide running out from Cleavel Point on the mainland, the other 55 metres projecting from Green Island. hey were 70 metres apart. Investigation suggests that, rather than being a causeway, the stone structures are the remains of two harbour piers. Timbers recovered from the mainland pier have been radiocarbon dated to circa 300 BC, the middle Iron Age, making it the oldest constructed port in North West Europe, and matching the radiocarbon date on the Poole Harbour log boat (UID 457515). (5-6)
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