The vaunted engineering skills that the Romans spread across Europe are supposed to have vanished during the "Dark Ages" - from the collapse of the Roman empire in the fifth century until about A.D. 1000. But a new find in the west of Ireland is challenging that assumption. A pair of underwater archaeologists has discovered the remains of a huge wooden bridge across the river Shannon. At 160-meters long, it my be the largest wooden structure from the early medieval period ever found in Europe, and its technical complexity has surprised archaeologists. Researchers now believe that the bridge, dated at A.D. 804, was the work of monks from the nearby town of Clonmacnoise, who kept Roman expertise over the centuries.

"The Clonmacnoise bridge fills an important gap," says archaeologist John Bradley of the National University in Maynooth. "There was no evidence, of large bridges in Europe between the Roman era and about A.D. 1000." It is unlikely to be the last such discovery, adds Morgens Schou Jorgensen of the National Museum of Denmark, an expert on the large wooden bridges built by the Vikings several centuries later. "I think that other similar bridges will now be found in Ireland, as happened in Denmark after the first Viking long bridge was uncovered in 1932," says Jorgensen. If so, the finding could mean that a sophisticated land communications network may have been in place across Ireland in the 9th century.

Donal Boland and Mattie Graham, divers who specialize in underwater archaeology, had begun their survey of the river Shannon after coming across an intriguing reference to abridge in the Annals of Clonmacnoise, written in 1158. They concentrated on a 500-meter stretch of the river near the remains of the monastery. In 1994, with archaeological guidance from Fionnbarr Moore of the National Monuments Service of Ireland, they found what they were looking for: an ancient oak post sticking out of the muddy riverbed. By last fall, Boland and Graham had discovered a total of 130 timbers, all nearly arranged in pairs 5 meters apart, spanning the entire 160-meter width of the Shannon. They also found nine oak dugout canoes, from which workers may have driven the pilings deep into the riverbed, and the remains of an elaborate horizontal cross-bracing system that once supported a roadway.

The line of the posts ran directly into the ruins of a13th century Norman castle, leading the researchers to suspect at first that the bridge was also a Norman construction. But this theory was ruled out after they sent samples of the oak timbers to Queen's University Belfast for dating by tree-ring analysis. The Belfast researchers, led by Mike Bailie, said the timbers were felled in 804, a full 365 years before Norman invaders arrived from France.

The focus of archaeologists then turned to the thriving 9th century monastic settlement at Clonmacnoise. The town of several thousand inhabitants straddled the point where an east-west route across Ireland known as the Eiscir Riada or Esker Read, crossed the Shannon. "The bridge was built to attract commerce" says Aidan O'Sullian the archaeological director in charge of Clonmacnoise, "and the leadership for the project was probably provided by the monks."

The discovery of the Clonmacnoise bridge has led archaeologists said, as Bradley to question whether knowledge was really lost in the aftermath of the fall of Rome, at least in distant parts of Europe that were spared the chaos of the Dark Ages. "We know the Irish preserved Roman texts, and this find suggests that they may also have preserved Roman technology and bridge building skills," says Bradley. "Perhaps the Dark Ages were not so dark after all."

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