British Archaeology, no 20, December 1996: News

The distorted timbers of the medieval boat raised last year at Magor Pill in the Severn Estuary have begun to produce intriguing clues to the boat's final few hours, during and after its shipwreck around 700 years ago.

The cargo vessel - one of the most complete surviving medieval boats known in Britain - may have sunk partly because of a split plank, found on the port side of its hull. The plank had previously split and been repaired, but had split again. It had fractured at the `stress point' where it had been made to curve up from the base of the boat to form part of the side. According to the excavator, Nigel Nayling of the Glamorgan-Gwent Archaeological Trust, similar repaired splits are known from other flat-bottomed boats of the period, suggesting it was a recurring problem.

The boat's cargo of iron ore was found to have shifted - which may also have contributed to the shipwreck - and the boat was covered in gravel, suggesting it may have foundered on a bank in a storm, which then whipped up the gravel to cover the wreck.

Evidence has also been found of salvage work at the boat immediately after its shipwreck. Axe marks at the bow end and elsewhere suggest locals may have recovered the stem-post - the forward-curving timber of the prow, which was complex to make - as well as the mast step (the timber block that carried the mast) and a few other items. `They probably didn't attempt to recover any of the cargo, perhaps frustrated by the gravel,' Mr Nayling said.

Timbers from the boat, dated by dendrochronology to 1239/40, were of a type of oak suggesting the boat may have been built in the Severn region; but it also contained one reused plank of Irish timber, perhaps from an Irish vessel broken up nearby. The lack of evidence for a deck, and the boat's relatively short length of about 15m, suggest it was not intended as an ocean-going vessel, but as one largely confined to the estuary and tributary rivers.

At the bi-annual British Archaeological Awards ceremony last month, the `sponsorship citation' for `best private-sector sponsor' for an archaeological project was won by Laing-GTM, the construction consortium that raised the boat using a giant excavator and a cradle. The boat's original timbers are now undergoing conservation at the National Museum of Wales, where last month a life-size model of the boat was delivered to aid research. The model, built by naval architect Edwin Gifford - who has also built half life-size models of the Graveney and Sutton Hoo boats - is expected eventually to be put on display in the musem.

Evidence that early building work at the Tower of London was grandiose but sometimes perhaps incompetent has come to light during excavation work in the moat this year.

Most telling is the discovery of the base of a square stone tower in the middle of the moat, on the western side. The tower, interpreted as part of Henry III's construction work in the first half of the 13th century, was used to carry a timber bridge - parts of which survive - from the inner curtain wall to Tower Hill. According to the excavator, Graham Keevil of the Oxford Archaeological Unit, the stone was of `very fine quality marble and sandstone in immaculate condition', preserved by the silts of the moat since the 13th century. However, the bridge was built without timber piles and showed dramatic evidence of subsidence - tilting about ten per cent across a length of less than 7m. The subsidence suggests this tower may be the one referred to by the 13th century chronicler Matthew Paris, who described the Tower gateway collapsing twice in 1240 and 1241.

Traces have also been found of a second dismantled causeway in the south-eastern corner of the moat, which was removed in 1680 to aid the flow of water. This causeway was found to be supported on beech piles still containing bark, giving an exact felling date of 1276. This date matches the documentary record, contained in pipe-rolls, of Edward I's construction work in the 1270s. Additional excavation of Edward I's main causeway across the moat - later rebuilt and still in use today - has shown that he too used very high quality ashlar masonry, much of which survives encased in later work. `His work was much more complex and of better quality than the later rebuilds,' Mr Keevil said.

The excavations form part of a Lottery-funded scheme to improve the setting of the Tower of London, which may eventually include the reflooding of the moat.

The prehistoric builders of stone circles and other megalithic monu-ments may have had an easier task than has traditionally been thought, according to an engineer from Oxfordshire.

Previously, archaeologists have supposed that dozens, if not hundreds of people were needed to lift the upright and horizontal stones at monuments such as Stonehenge or the Early Neolithic `portal dolmen' tombs - such as Pentre Ifan in Wales - where a heavy `capstone' rests on three uprights. However, the engineer Cliff Osenton, from Banbury, claims that only a handful of people were needed to build most monuments, suggesting that small settlements could easily have built their own megalithic tombs.

In a demonstration last month in a stone quarry in the Cotswolds, Mr Osenton showed that one man could lift a rough-hewn, 5-tonne block of sandstone about 2ft off the ground in around two hours using only a 12ft wooden pole, with a second man stacking wedges underneath the stone. Using this system, only one man would have been needed to lift a typical portal dolmen capstone in a few hours; two to raise a Stonehenge lintel; and only eight to raise the massive uprights of the Stonehenge trilithons, each weighing about 40 tonnes.

The system, which is unpublished, is similar to one proposed at Stonehenge years ago, in which a stone is jacked up bit by bit one side after the other, and supported on a pile of timbers. The critical difference in Mr Osenton's system is that the supporting timbers under the stone are placed in a triangular formation, in such a way as to allow the stone to wobble slightly and grant maximum advantage to the lever. By this method, the capstones of portal dolmens would have been raised before the uprights, which were fitted in later. The uprights can be raised in a similar way, according to Mr Osenton, with the base resting against a trench into which the stone is dropped, with a post at the back to direct and support the stone on its way down.

Witnessing the demonstration was Dr Aubrey Burl, a leading authority on stone circles. He said it was `very interesting' and clearly showed that a capstone could be raised by very few men. `Portal dolmens have always been seen as family tombs because of the small size of their chambers. But it was not clear until now how a family could have built one,' he said.

The idea that the capstone was raised before the uprights also makes sense of the fact that one upright in a portal dolmen is usually pointed, Dr Burl added. `That allows the capstone to be swivelled from that upright onto the other two.'

He said he doubted, however, that uprights were raised by Mr Osenton's system, requiring a single supporting post at the back of the trench. `As far as I am aware no-one has found evidence for a post-hole in that position,' he said.

Awards 1996

High achievement in British archaeology was recognised again this year in the biennial British Archaeological Awards ceremony held last month.