Monument record MDO7455 - Green Island Causeway, Cleavel Point, Poole Harbour, Corfe Castle

Buried remains, mostly below the low water mark, of a stone-ramped structure connecting Cleavel Point to Green Island with a gap in the centre of the channel. The structures are partially visible on aerial photographs of 2008.

(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>

A causeway between Cleavel point and Green Island with a gap in the centre of the channel. Its identification as a causeway was long known in local legend but was confirmed as fact when investigated in the Summer of 1959 by the Dorset Natural History and Archaeological Society with the Dorset Boy Scouts Association. Taunton sub-aqua club examined the causeway underwater. The investigations found stone flags lying on flint and stones. Pieces of wood were recovered too. They were found to be bedded in the causeway underneath the limestone flags lying side by side longitudinally. The wood was not suitable for dendrochronological dating. No evidence for a collapsed under water bridge or structure was found in the gap in the causeway. The purpose and date of the causeway is unknown, but it is thought likely to be medieval. It is mentioned in Hutchins history as a bridge the remains of which were visible n 1774. Hutchins records that Green Island was once connected to the Ower peninsula by a bridge, the remains of which were visible in 1774. While a medieval date is suggested, it is not impossible that it may date even to the Roman period. <3-4>

RCHM record this feature under `Roman' and add that 'the causeway, undated, was probably surfaced with stone flags on a log courduroy laid axially'. <5>

The causeway is below water level except when tides are particularly low. The structure can be traced leading from Cleaval Point and from Green Island but its central section (if this existed) has been destroyed by the South Deep. <7>

The causeway was investigated again in 2000 and 2001. <8>

A summary of recent work is given in Dorset Life, who commissioned some carbon dating of some timber piles. The results were of a Middle Iron Age date. <9>

The site is also recorded by the DCF MAD comprising both the mainland end and the island end. <10>

Two linear banks at either end of the causeway were plotted during the South West Rapid Coastal Zone Assessment Survey (Dorset) from aerial photographs of 2008. The banks measure 14 m by 3 m and 21 m by 5 m. <11>

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. They 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).
Bournemouth University, Dorset Coast Digital Archive. '3. Managing the coast. History on the seabed.' <<http://www.dcda.org.uk/3-2history/3detailed.html>> [Accessed 26-AUG-2010]
Poole Harbour Heritage Project Ltd. 2010. Poole Harbour Heritage Project. <<http://pooleharbourheritageproject.org/>> [Accessed 26-AUG-2010]

Markey, M, 2012, An Iron Age Port in Poole Harbour, Dorset (Unpublished document). SDO21383.

<1> Poole Harbour Board, Poole Harbour (Map). SDO20476.

<2> Field, N H, Oral: Letter from Norman Field, and tracing 17 9 1956 (Verbal communication). SDO19374.

<3> Boy Scouts Association, 1959, Green Island Causeway Poole Harbour. (Monograph). SWX8058.

<4> Bugler, J, 1966, Poole Harbour "Causeway". Proceedings of the Dorset Natural History and Archaeological Society 88, 158-160, p158-160 (Article in serial). SWX7343.

<5> Royal Commission on Historical Monuments (England), 1970, An Inventory of Historical Monuments in the County of Dorset, Volume II (South East) Part 3, 597 (Monograph). SDO150.

<6> Papworth, M D J, Trust for Wessex Archaeology, 1983, Isle of Purbeck Survey, IOP 54 (Index). SDO147.

<7> Markey, M, 2000, Green Island Causeway 2000 fieldwork. (Unpublished document). SWX8107.

<8> Markey, M, 2001, Green Island Causeway 2001 fieldwork. (Unpublished document). SWX8106.

<9> A'Court, M, 2003, Poole - the oldest cross-Channel port in Britain? (Article in serial). SWX4526.

<10> Le Pard, G, 1995-2003, Dorset Coast Forum Maritime Archaeological Database, Structure 4 & 20 (Digital archive). SWX8707.

<11> Channel Coastal Observatory, 20-JUL-2008, CCO Aerial Photographic Coverage 2008 (Aerial Photograph). SDO12674.

<12> Royal Commission on Historic Monuments, Externally held archive: RCH01/093 RCHME Inventory: Dorset II (South-East) (Unpublished document). SDO17434.

<13> National Record of the Historic Environment, 457510 (Digital archive). SDO14739.

Record last edited

Apr 1 2025 11:40AM