Mary Zacaroli talks to archaeological artist Clara Semple about the mythical silver coin known as the Maria Theresa thaler

Archaeological artist Clara Semple has spent more than 40 years working in numerous Arab countries on both sides of the Red Sea. Almost whereever she went, she came across large silver coins bearing the portrait of Austro-Hungarian empress Maria Theresa, which over the centuries have gained near-mythical status across the Arab world.

Her beautifully-illustrated first book, A Silver Legend tells the story of the coin, known as the Maria Theresa thaler. As well as being used as currency, it was incorporated into ethnic jewellery. She said: "Women saw it as a protection, a fertility symbol and it was a way of wearing their wealth, but it was also their dowry and they got to keep it after a divorce."

Having first come across the jewellery in Saudi Arabia in the early 1970s, when women were selling their silver ornaments to buy gold, Clara then saw piles of the thalers in a huge souk in northern Yemen. "They were being sold for Kalashnikovs and arms of all sorts, daggers and washing machines," she said. After that, she began to notice the coins wherever she travelled, even in Africa.

She began to ask questions about the coin and became increasingly interested in its history. So why did she write the book? "I thought it was a very romantic story, especially because most people didn't quite know where this coin came from," Clara explained. As a trade coin, it is fascinating to economists, cultural experts and historians although not to coin collectors, or numismatists. It is certainly not rare or valuable, since every coin has the same date, 1780 the year that Maria Theresa died and it is believed that over 400 million coins are in existence, with some estimates doubling that.

Maria Theresa was the only female head of the powerful Habsburg Dynasty, based in Vienna, and lived between 1717 and 1780. Known as the mother-in-law of Europe, she bore 16 children and was something of an enlightened despot. The thaler depicts her in later life. The coins became so popular that after she died, the Vienna mint continued to churn out millions of them and still prints a small number for collectors today.

For more than 200 years it was traded mainly around the Middle East and North Africa, although it reached practically all the continents of the world. Clara came across it in a market in Sarawak, Borneo, where although it wasn't used as currency, it was once used as blood money amongst the head hunters. Because of its silver content it had a real value, and it was traded like any other commodity. Eventually it became valued as a coin, too. It was only in the 1960s that the thaler was finally superseded by other forms of currency in the Middle East.

Even so, rumours abound that hoards of them are hidden away as it's safer to keep one's wealth in silver, rather than paper money.

In the 1930s, Mussolini started minting coins for his adventures in Abyssinia (present-day Ethiopia), so various other countries decided to mint their own version, too. "The British wanted to supply them for their commercial interests and politically for their military operations in Ethiopia," Clara explained. "They decided that this wasn't a coin at all, but a piece of silver because Maria Theresa had been dead for hundreds of years and the Habsburg Empire had been dissolved, so they could copy it."

An interesting anecdote in the book describes how Langford Jones, a master engraver who lived in Blewbury, near Didcot, modelled a replacement or, as he termed it, a fairly competent forgery'.

As for the intriguing Ms Semple, her story is as interesting as the thaler's. Born in Sri Lanka, she was brought up in South Africa and trained as an artist. She came to England in her early twenties and became an archaeological artist by accident." I went out and joined an exhibition in Cairo and was so smitten with the whole place that I stayed on there and worked all over Egypt on many excavations," she said.

She worked in several temples and tombs on the Nile in Egypt and the Sudan. "It was terribly exotic," she explained. "Sometimes I lived in the temples, but I also lived on a Nile steamer, sort of Agatha Christie-style."

At one time, she was living in one of the temples just north of Khartoum in the Sudan. "I had to drive myself over hundreds of miles of desert to get to work on my own." Having owned a house in Oxford for 30 years, she is now based here permanently. Married, with two grown-up daughters, in some ways she reminded me of a very feminine Indiana Jones. What a shame that she has no plans to write her own autobiography.

  • A Silver Legend is published by Barzan Publishing at £19.95.