Gems in Dublin's old debris

THE robust run of winter storms has planed the strand to its lowest level and polished it clean as a bone. The surf ran up to chew at the dunes a bit more, and walking beside the high, raw cliffs of sand, I hope, as always, to find something from the past sticking out.

Once, on this strand, a visiting friend found a 14th century bronze pot - well, half of it. And in the dunes along at the mountain there's a new drift of limpet and winkle shells that could be somebody's midden - Mesolithic, medieval, or whatever. But for the moment I rest content with another 20th century plastic fish box, and a trawlerball from the Faroes in a novel shade of pink.

Fish boxes ("Unauthorised Use Forbidden") are splendid for growing herbs in outside the kitchen door; but plant growing containers have changed with the ages the people of Viking Dublin could, I suppose, have used old wattle baskets, lined with moss to hold the soil, for the plants that figured so largely in their lives.

They lived close to nature in so many ways, some of them surprising and ingenious. Archaeologist Siobhan Geraghty means no insult when she describes their settlement as "a very large and rich compost heap, over 18 hectares in area and more than three metres deep. The town which flourished on top of this bacterial and fungal power station . . . was quite unlike any habitat which now exists."

Ms Geraghty was one of the National Museum team who joined Dr Patrick Wallace (now the museum's director) in excavating Wood Quay. Her new book, Viking Dublin Botanical Evidence from Fishamble Street, is a remarkable piece of environmental archaeology - further proof, if it were needed, of the great "forensic" potential of a site so nearly lost to Irish history.

Her evidence, mostly seeds and other plant remains, was sifted from precious organic material, salvaged speedily in blocks, double wrapped in plastic, and stored in the dark until it could be teased apart under the museum microscope.

Much of the dark, peaty stuff was made up of wood chips - 10 cubic metres or more packed into the foundations of each new house, so that over a period of some 60 years, the ground level of Fishamble Street was raised by more than a metre. As the mass of chips slowly fermented and decayed, they served as free underfloor heating - part of the compost heap effect that would have made Viking Dublin a "heat island", as cities are today.

The surface carpet of the floors was a soft, organic mix of wood chips and leaf litter - not the rushes or straw we may have imagined - and it was regularly cleaned off and renewed, like the sawdust of bygone butchers' shops. There was a constant littering of shells from hazel nuts (opened with a knife I must try this), and more whole nuts got lost among the springy brushwood that topped the earthen benches - "down the back of the sofa".

This medieval muesli was part of a very well balanced diet a lot of chewy wholemeal bread (so coarse and chewy it wore down the teeth) supplemented by fruits, nuts and beans, some meat and fish, shellfish, eggs and dairy produce. The Vikings ate their apples whole - no nibbling at cores - and were so uncorrupted by sugar that sharp sloes and rowan berries were as palatable as blackberries and fraughans.

Much of the evidence for diet comes from sorting the sludge in the backyard cesspits, still foul smelling after almost 900 years. Sewage is an issue "not much discussed by historians", as Siobhan Geraghy point out, but she doesn't shrink from telling us that the Viking Dubliners wiped their bums with woodland moss in large quantities - perhaps 15 tons a year for a town of some 900 houses and 4,500 people.

Some of the cesspit seeds are from cereal weeds now scarce or extinct in Ireland - the mildly toxic corn cockle, for example and corn marigold, which has almost totally yielded to herbicides. Other seeds among the 94 species speak for the rank, weedy growth of the fenced backyards and alleys of the town.

Henbane, for example, one of the medicinal and magical plants used by the Vikings, was common in towns until the 17th century and is now in dramatic decline. Black nightshade was another common, nitrogen hungry weed, now a somewhat erratic survivor in tilled ground.

Given the special nature of the Viking Dublin habitat, says Ms Geraghty, it's surprising that more than 50 of the species still grow in the inner city - stonecrop, for example, which may have been encouraged to grow on the sod roofs as a fire suppressant, or fat hen, the seeds of which were sold by hawkers or grown for a leafy vegetable.

The vegetables grown in the backyards are largely missing, from Ms Geraghty's study. There were probably cabbages, leeks and onions, but their remains, recovered from cess pits, need better identification than a lowpowered microscope can give. Only the beans (grown, like most of the flax, in fields outside the town) left skins that showed up under the lens.

The seeds of Fishamble Street - from pits and floors and roofsods - say much about the farming hinterland, with grassland for cattle, and arable crops. There may have been haymaking (often thought a Norman introduction) and, if not, then flood meadows to preserve grass under winter. The grain harvest for the town - wheat, barley and oats, cut with sickles - probably took at least 10,000 acres (4,046 ha) - more if beer was being brewed.

The houses lasted only 10 or 15 years and 50 or more were built every year. Each used the wood of more than 15 trees, thousands of metres of hazel wattles, posts and brushwood, tons of fuel wood. It's in such simple, but graphic accounting that Ms Geraghty measures the remarkable impact on nature of one small early medieval town.