What is the secret of Tintin's plus-fours?

Did Tintin start his adventures as a Roman love god? When the Belgian cartoonist Hergé sketched the popular adventures of the boy reporter, he acknowledged sources as diverse as the National Geographic, Jules Verne and even movies by the Marx brothers, including Duck Soup and A Night at the Opera.

But two Spanish researchers are trying to prove the spirited cartoon hero was inspired by a statuette of a priapic Roman god in an archaeological museum in the Catalan coastal town of Tarragona.

A design teacher in Barcel-ona, Rita Gual, and her artist sister Laura, began their quest after noticing an oval-faced figure in a glass case at the museum. Striding with a purposeful gate recognisable to Tintin fans the world over, the statuette is topped out with a broken ring bearing a striking resemblance to the boy reporter's distinctive quiff.

Looking up exhibit 542 in the museum's catalogue, the sisters were astonished to find its attribution as a Tintinnabulum: a phallic Roman figure decked out with bells to hang at the entrance of the family home to invoke good fortune and prosperity. So the Guals embarked upon a months-long research project to unearth possible links to Hergé's famous character, the protagonist of some two dozen adventures published worldwide in 27 languages and dialects.

The Belgian author long said the character was inspired by Tintin-Lutin, a cheeky lad with a rebellious tuft in tales by the French caricaturist and designer Benjamin Rabier. But the sisters believe there is a strong possibility Hergé could have seen the Tarragona figurine, or a similar one unearthed at Pompeii.

The sisters say the author left an unfinished adventure, Tintin and the Alpha-Art, after he died in 1983. This was set in Naples, where a similar Tintinnabulum statuette is held in the national museum.

"There are so many formal coincidences," Rita Gual said. But one glaring attribute of the statuette is overlooked: a swollen phallus so large it almost brushes the ground. How do the Guals reconcile this with Tintin? Of course. The capacious, plus-four breeches.