Professor Helga Seeden runs her hands over its body. "Late Roman," she remarks. "They probably used it above a door lintel." Two labourers arrive with a Roman capital, a marble block of vine leaves that toppled off a column lying in the mud outside, probably knocked down by the earthquake that levelled the Roman city of Berytus in AD551. A mile away across the civil-war ruins, Muntaha Beydoun has discovered what may be evidence of that same disaster: a disruption in the sediment of the earth, the impact of a tremor that must have occurred between AD150 and early Medieval times.
Perhaps it is this pattern of calamity that makes the Lebanese so frightened of their history. They have still not examined the reasons for the civil war that ended four years ago - the Beirut newspapers refer to that conflict and its 150,000 dead as al-hawadess, "the events" - and this unwillingness to deal with the demons of history has manifested itself in one of the most exciting archaeological digs in recent Middle East history. There's an almost palpable nervousness about what might be found, a feeling that something unpleasant may lie buried there which tells the Lebanese too much about themselves.
The destruction of Beirut has presented historians with the opportunity of unearthing the ancient streets and 2,000-year-old houses of a capital city before the demands of modern reconstruction destroy them for ever. The finds already have been remarkable. Mameluke perfume jars, an Ottoman silk factory, Byzantine plates, amphoras and Roman roads and mosaics and columns, part of what one archaeologist claims is the original 3,000- year-old wall of Phoenician "Brt" - pronounced "Birut", the "place of wells" - have emerged from Lebanon's red clay.
Although many of the archaeologists are Lebanese, the site workers are Syrian, earning $10 (£6.40) a day. "Lebanese young people are too busy making money to help us," one of the foreign archaeologists said."They don't feel strong roots towards their history because they think it has been so bloody in the past and the present."
Prof Seeden, a German, came across a different form of unease when she asked the Muslim religious authorities for permission to dig beneath their ruined property in the city centre. "They said: `No, absolutely not - we don't want any excavations, because all the archaeologists are going to find are Roman remains.' It took me a long time to explain to them that we are also digging up Islamic history."
Seventy-five years of Christian-Muslim historical disputes had provoked concern. Even before they gained their own state under the French mandate in 1920, Christian Maronite writers had argued that the region of Lebanon was, in spirit and culture, Phoenician and Roman rather than Islamic and Arab - that it was Western rather than Oriental; Muslim academics said the Phoenicians were Arabised in antiquity and Lebanon was Arab and thus should have remained part of Syria. The 1975-1990 civil war was, in one sense, fought between Christians who believed Lebanon was a Western nation and Muslims who regarded themselves as Arab nationalists.
Hence the Islamic authorities' fears that Beirut's archaeologists were only going to reassert Maronite claims to Lebanon's glorious Roman past. Unfortunately for them, the Omayad, Abbasid and Mameluke periods have yielded fewer treasuresthan the ages of Rome and Byzantium.
The Romans drank the same mellow red wines as the Lebanese produce today in the Bekaa valley. The Byzantines blew the same blue glass as the Syrians and Lebanese produce today. Cosmetic jars suggest Beirut's women valued their beauty as much as Lebanese women do now. In the border of a mosaic south of the city, its Byzantine owner had ordered to be written the words: "I paid for this." The Lebanese, it seems, had always enjoyed a display of their wealth.
But historically, Beirut was a city of blood. The AD551 earthquake killed almost the entire population; the Crusaders massacred the inhabitants when they refused to surrender; its people died in their thousands in the Turkish famine of 1917. Most of the 150,000 dead of the civil war were killed in Beirut - around 10,000 of them in Israel's 1982 invasion - but the archaeologists have found not a single human bone. Yet, beside what she says is the Phoenician wall, Professor Leila Badr has come across the ashes of a terrible fire that raged 4,000 years ago. There are other tide-lines of burning deep in the earth.
Is this what the Lebanese are afraid of? That these gentle, artistic people contained within themselves the seeds of self-destruction, buried now in a history which the Lebanese are too frightened to explore? The Prime Minister, Rafiq Hariri, has donated $1m to the digs but Solidere, the city's reconstruction company, gave its full support to the archaeologists only when it realised the amount of money that could be made from tourist archaeology.
"The real problem is that people don't change," a Lebanese archaeologist said. "Way back in the past, our city-states were always fighting each other ... In the civil war, Christians and Muslims fought each other, sometimes people from neighbouring villages killed each other. And when Alexander the Great besieged Tyre, it was the people of Sidon - only 20 miles to the north - who built the causeway for him so he could capture the city. People don't want to be reminded of this facet in their characters. So they are suspicious of history."
El-Fadl Shalak, head of the Lebanese Council for Redevelopment and Reconstruction, admits to the fear the Lebanese have of their past. "We are frightened of our history because we are not united in our understanding of it. If you dig three feet down, you find Muslim remains and the Muslims are interested in this. If you dig six feet, you come to the Roman, then Phoenician remains ... What we've got to realise is that it's all part of the same story. We have got to learn that the past and the future must be connected, that there were good, peaceful times as well as bad times. Only in this way can we learn to understand ourselves."
For some, the lesson comes too late. In the Metn hills, archaeologists discovered that a new church had been built with old stones. Then they found that a nearby Roman temple had disappeared. Local Christians had simply bulldozed history away to build their church.