Archaeologists in Portugal have discovered peppercorns, fragments of Chinese porcelain and bronze cannon among the sunken remains of a 400-year-old ship that once sailed the spice route between Europe and India.

The wreck of the still-unidentified vessel was found at the beginning of September by a team of experts surveying the area around the town of Cascais, about 26km west of Lisbon.

The wreck site, which sits about 12 metres below the surface, is about 100 metres long and 50 metres wide.

The teams say the discovery will shed light on both Portugal’s trading past and Cascais’s place within it. “We found the ship on 4 September, using a geophysical survey and divers, and spent four days working on the site,” said Jorge Freire, a maritime archaeologist and scientific director of the underwater archeological survey.

He said divers had also come across cowrie shells, which were used in the slave trade.

“We don’t know the name of the ship, but it’s a Portuguese ship from the late 16th or early 17th century,” he said, adding that the team had been able to put a rough date on the wreck as the cannon bore the Portuguese coat of arms and the porcelain belonged to the Wanli period (1573-1619).

“It tells us a great deal about Cascais’s maritime history and identity,” said Freire. “It’s like we’ve been telling the local people here: this is a great discovery and its greatness lies in what it – and the artefacts – can tell is about the cultural landscape.”

The pieces will now be examined by the Portuguese government’s directorate-general for cultural heritage.

The mayor of Cascais, Carlos Carreiras, described the discovery as one of the most significant archaeological finds of the past decade. He said that although the cargo ship had yet to be identified, it could prove significant to the town.

“It’s an extraordinary discovery that allows us to know more about our history, reinforcing our collective identity and shared values,” said Mr Carreiras. “That, in turn, will certainly make us more attractive and competitive.”

The discovery comes 24 years after experts found the wreck of the Nossa Senhora dos Martires (Our Lady of the Martyrs), which also sailed the spice route and sank off Lisbon in 1606.

According to the survey team, who have been mapping the areas since 2009, the latest wreck is in better structural shape than the Nossa Senhora dos Martires. – Guardian