"Join Marilyn in the drain," instructed the site supervisor when I pitched up at Vindolanda, a partially excavated Roman fort near Hadrian's Wall. "First dig then scrape. You don't want to miss anything."

No indeed. This was a first encounter with the world of archaeology. So it was into the drain to sift, scratch and dig.

This was not an occupation that fired my imagination until I discovered that volunteers could sign up for an annual dig at Vindolanda. "Want to excavate at one of the top Roman archaeological sites in Britain?" read the website headline. With visions of unearthing Roman treasure I packed a waterproof jacket and boots and headed for northeast England.

The annual dig, which takes place during the northern European spring and summer, had been in progress for several weeks by the time I arrived.

"Spoil heaps" of discarded dirt and rubble were mounting around the diggers. The ratio of digging to treasure-finding appeared to be heavily rubble-oriented.

"You can dig for days without finding more than a few dog bones, said my drain mate Marilyn cheerfully. "It can be like looking for a needle in a haystack."

But the prospect of finding the needle had clearly hooked Marilyn. For the fifth year in a row she was back in Vindolanda with a now discerning eye for unearthing fragments of England's past. She enrols each November for the following year when applications open on Vindolanda's website. Places fill quickly.

Vindolanda was already a bustling fort housing a military and civilian population before Hadrian's Wall was built in AD 122 across the northern frontier. The original turf and timber fort was erected in the late 80s near the centre of the frontier and during the next three centuries was replaced with increasingly larger, more solid structures.

Vindolanda troops played apivotal role in policing the movements of tribes within the border region and regulating commerce between Roman Britain and its barbarian neighbours.

When the collapse of Rome's western empire in the early 5th century brought its long hold on Britain to an end, Vindolanda fell into ruin. It was not until the middle of last century that the story of the people who had begun living there soon after the time of Christ began to unfold.

It's a story that unfolds like an absorbing soap opera, says deputy director of excavations Justin Blake. After 13 years of working full time at Vindolanda he has come to know the cast and characters of the people who lived on Britain's northern frontier. "You start out looking for fragments of lives gone by but when you begin piecing them together the people of Roman Britain come alive" he says in his lilting Northumberland brogue.

Justin had dropped by the drain to see if I had produced more than sweat and dirt. By way of encouragement he explained how he first came to Vindolanda as a reluctant teenage volunteer needing to keep fit for the school rugby team. He dug up a bronze coin dating from AD 106 and the hairs on his arms stood on end thinking about the person who lost it. He ditched plans to become an RAF pilot and enrolled for a degree in archeology at Durham University.

The most remarkable insights into the community of Vindolanda came with the excavation in the 1970s of letters written by commanding officers, their wives, soldiers, merchants and slaves. Known as the Vindolanda tablets, the letters were written in ink on postcard-sized slivers of wood and date from the time of the earliest settlement. Complete with spelling mistakes and occasional slang they depict life on the edge of the Roman world, revealing not only what a well-oiled machine the Roman Army was but much about the civilian life on Britain's northern frontier.

Most evocative of the letters is a famous birthday party invitation letter from Claudia Severa, wife of a commanding officer, to her friend Sulpicia Lepidina. Stuck far from home on a Roman frontier with few associates of her social standing, she longs for the company of her friend. Her letter is the earliest female handwriting to survive in Western Europe.

Discoveries like the Vindolanda tablets don't come along every day in the painstaking world of archeological excavations. But just days before I arrived volunteers had unearthed the most exciting treasure since the tablets, a carved shrine dating from the 3rd century. "A rare find," confirmed the visibly moved Andrew Birley, director of excavations at Vindolanda and son of Robin Birley who discovered the famous writing tablets.

The 30 volunteers on my dig ranged in age from 17 to 77. When lunchtime came round they buzzed about the morning's work. Alice Constable, related to the famous 19th century English Romantic painter John Constable, had dug up a piece of pottery decorated with a bird and dog. Peter from Bristol held up his prized find of the day, a piece of bottle blue Roman glass.

Kevin, a Glaswegian jazz musician with a passion for Roman history, looked wistful as he handed over his most prized find, a Roman phallic symbol. The discovery caused him to sign on for another two weeks dig.

By lunchtime I had no more to report than the discovery of a fragment of pottery and my disappointment when a flash of filigree-coloured soil turned out to be dust. So it was back into the drain with the remains of the day to strike it lucky.

Danny Rolet, another drain-mate, paused from her toils to inspect a small, unusually shaped rock I hoped would turn out to be something significant under its dirt encrusted surface. Declaring the item to be unadulterated rock she explained sympathetically that a fool's gold experience is not uncommon at archeological digs.

My confidence was boosted when another half-hour's dig unearthed a Roman nail. The most inspiring nail I had ever seen. Keep digging.

A couple of hours later, and not wanting to succumb again to the fool's gold syndrome, I nearly tossed out the shovel of dirt which contained a small spot of greenish soil. Sift just in case. I felt a rush of adrenalin. A round shape emerged from the green soil. It felt hard beneath its dirty exterior.

Andrew Birley inspected the item and pronounced it "quite a find." A Roman coin dating, he guessed, from about the 3rd century.

I held the little coin, not much bigger than my thumbnail, and felt emotional. In 1700 years I was only the second person to touch it. What was the person like who lost the coin? Would they have cursed the loss or brushed it off? For a moment time past felt like time present.

The age of the coin corresponded with the current excavations of 3rd century buildings at Vindolanda. It must have washed down the drain we had been set to work in.

Bearing in mind the advice that you can dig for days without finding anything of significance, it was hard not to feel I'd struck gold.

The original fort lies several more metres under the ground, which means the story of the Vindolanda people will continue to unfold in years of digging to come.

Getting there: Air New Zealand operates daily direct flights to London via Hong Kong.

National Rail services from London to Newcastle take approximately 3.5 hours.

Digging: Volunteer programme runs from April through to the third week in September. See vindolanda.com.

Where to stay: The Twice Brewed Inn is 10 minutes from Vindolanda.

Further information: For general information about visiting Britain see visitbritain.co.nz.

Susan Buckland visited the UK with the assistance of Air New Zealand.