Here is how a several centuries–old coin may rewrite a key chapter in the history of ancient India: In 1851, a hoard of gold coins issued by several kings from the Gupta dynasty was unearthed near the holy city of Varanasi, in northern India. The Guptas, who ruled from the 4th to 6th centuries AD, ushered in the Golden Age of ancient India, a blossoming of the arts and sciences that produced the concept of zero, a heliocentric astronomy, and the Kama Sutra.

Gupta kings stamped their given names on the front of their coins and, on the back, an assumed name ending in “aditya,” or sun. On two of the coins in the hoard, scholars were able to read only the king’s assumed name—Prakasaditya, or splendor of the sun—but it seemed obvious that these, too, were Gupta coins. Few scholars disagreed. Without the given name, however, the mystery would remain for more than 160 years: Which Gupta king was Prakasaditya? When did he rule?

Ancient Indian coins conjure up marketplaces along the Silk Road, the trade route that connected the East and West; conquerors and their traveling mints; wars; and lost kingdoms.

Pankaj Tandon is a Boston University associate professor of economics by training and, by passion, a scholar of ancient coins—or numismatist. In 2010, Tandon, who specializes in coins of ancient India, which to numismatists includes what are today Afghanistan, Bangladesh, Bhutan, Nepal, Pakistan, and Sri Lanka, set out to crack the puzzle of Prakasaditya. In 1990, an Austrian numismatist named Robert Göbl had speculated without substantive proof that Prakasaditya was a Hun, but most scholars had continued to regard the mystery king as a Gupta. Tandon began by scouring more than 60 images of the coin—additional specimens had been found over the years—but the coins had all been poorly made and not one image revealed the king’s given name.

Tandon spent the 2011–12 academic year in India on a Fulbright-Nehru fellowship, teaching microeconomics at St. Stephen’s College, his alma mater, in the capital of New Delhi. On weekends, he made road trips to several government museums in the nearby state of Uttar Pradesh to examine coins. On a visit to the Lucknow State Museum, he was given a rare, behind-the-scenes tour of an uncatalogued collection of dozens of Gupta coins. With no time for careful viewing, he hastily took pictures of the lot.

It wasn’t until he got home and sorted through the images that he realized that one of them was of the mystery coin. And here, at last, were all the letters he needed to read the king’s given name—Toramana. He was no Gupta. Toramana was a Hun, an invader whose conquests in northern India were believed to have stopped well short of Varanasi.

It was a surprising discovery. What were the coins of an archrival doing in the heart of the Gupta empire? Could the Huns have been responsible for the decline of the Guptas, in the second half of the fifth century?

Tandon returned to India in the winter of 2015–16 on another Fulbright-Nehru fellowship to pursue these and other numismatic questions. His work includes cataloging coins of the Guptas—and of their predecessors, the mighty Kushans—in the government museums in Uttar Pradesh, which have the largest collection of coins from these two dynasties after the British Museum in London, and the National Museum in New Delhi. Tandon has been invited to collect new information about the Kushan and Gupta coins for scholars in an updated print catalogue.

Numismatics plays an important role in understanding ancient Indian history, says Joe Cribb, former Keeper of Coins and Medals at the British Museum and renowned authority on ancient Indian coins. Here’s why: Surviving written texts that feature the ancient history of India were created as religious or literary texts. To reconstruct the past, says Cribb, historians look to other sources, such as archaeological finds and inscriptions on stone and metal. Coins offer another form of evidence, requiring similar care and expertise in the interpretation of engraved words, symbols, and images. “This is where a scholar like Pankaj comes in,” Cribb says, adding that the BU economist brings a rigorous scientific approach.

Tandon, who earned his PhD in economics at Harvard, corroborates his numismatic findings with information he gleans from historical texts, inscriptions, and even sculpture from old temples. He has published his research extensively in peer-reviewed numismatic journals. Cribb has invited Tandon to collaborate with him on a catalogue of Kushan coins for the British Museum.

Tandon began collecting coins as an investment in the late 1990s, when India was poised for growth. “As an economist, I know that in developing countries, the price of historically important cultural memorabilia is relatively low,” he says. “As the country becomes wealthier, the value of such memorabilia skyrockets.”

Once he acquired a coin, Tandon wanted to learn everything he could about it. As he immersed himself in the study of ancient Indian coins over a decade, their value went up, just as he had predicted. What he hadn’t predicted was that he would evolve from a collector into a scholar.

“Indian coinage is perhaps the most fascinating in the world,” Tandon says. “There are all these outside influences—from ancient Greece, Rome, Persia, and China—and there is all the indigenous evolution [of the coins themselves] over 2,500 years.”

Ancient Indian coins conjure up marketplaces along the Silk Road, the trade route that connected the East and West; conquerors and their traveling mints; wars; and lost kingdoms. They depict kings and deities and animals (Prakasaditya portrayed himself astride a horse, slaying a lion) and feature one or more scripts: Greek, the now-extinct Kharoshthi, and Brahmi, the mother of most modern Indian scripts. Early on, numbers were written using letters, and the system for writing dates varied across kingdoms. The seeming inscrutability of it all appealed to Tandon, who is a devotee of the New York Times crossword puzzle. He knew the Greek alphabet, and over time he taught himself to read Kharoshthi and Brahmi.

What Coins Tell Us About a Forgotten Dynasty

His first major acquisition was from a hoard of coins found in Balochistan, in present-day Pakistan, that had been issued by kings called the Paratarajas, who ruled the all-but-unknown kingdom of Paradan. They had issued copper coins with legends in Kharoshthi, and silver coins with legends in Brahmi. By scrutinizing the images and legends, Tandon came up with the chronology of the 11 Paratarajas rulers who, in all likelihood, ruled from around 125 to 300 AD. “Pankaj’s paper on the Paratas is an excellent example of the diligence and intelligence of his numismatic work,” says Cribb.

“Indian coinage is perhaps the most fascinating in the world. There are all these outside influences—from ancient Greece, Rome, Persia, and China—and there is all the indigenous evolution [of the coins themselves] over 2,500 years.” Pankaj Tandon

Tandon put the small kingdom back on the map. Then he dug up clues to help make it a living, breathing world. As an economist, he was curious about the source of the kingdom’s wealth. Searching through historical documents, he concluded that the secret of its prosperity was international trade. One export was a lavender-like plant called nard, which grew in abundance in arid Balochistan and fetched a high price from the Romans, who prized nard for its perfumery.

In 225 AD, the coinage of the Paratas went from silver to copper, a sign of the kingdom’s declining fortunes. Around the same time, with civil war raging at home, Rome’s trade with India suffered. The Roman economy was the biggest in the world, just like the US today, and a recession in Rome must have led to recession in India, Tandon hypothesizes. “Globalization may not be the modern phenomenon we think it is,” he adds.

Curating a Museum

Though he considers himself primarily a scholar, Tandon still collects coins. “You need to hold a coin in your hands and look at it from various angles to study it to your complete satisfaction,” he says.

Too often, though, when individual collectors acquire coins, they pass from public view and are unavailable for scholarly study. Twelve years ago, in an effort to help remedy the problem, Tandon established an online, or virtual, museum, CoinIndia, which features high-resolution images of nearly 2,000 coins from the Indian subcontinent, spanning some 2,500 years. Upinder Singh, the head of the history department at the University of Delhi, calls the website “a wonderful, unparalleled resource on the history of Indian coinage.”

One day, Tandon hopes, his own collection will be displayed in a real museum, ideally in India, where the coins were first unearthed.