DUBROVNIK, Croatia (AP) — A sunken 18th-century boat has been discovered by chance near the majestic stone walls of Croatia's medieval city of Dubrovnik.

Ivan Bukelic was working on a water pipeline in Dubrovnik's old port back in April when he found a wooden structure buried in the seabed.

“I can now say I discovered a boat at the Old Town Dubrovnik,” Bukelic, who is a diver and undersea builder from Dubrovnik, said.

He added the vessel was some 60-80 centimeters (23-31 inches) under the sea bottom.

A key trade port in the Adriatic Sea in medieval times, Dubrovnik has been declared a UNESCO protected heritage site. It attracts huge crowds of tourists, especially during the summer, and is also known as a filming site for HBO’s Game of Thrones series.

The remains of the boat in Dubrovnik's old port have been protected for further examination.

“We still cannot speak of the type of vessel or its dimensions but we can say for certain, based on the results of radiocarbon analysis that it was from late 18th century,” marine archaeologist Irena Radić Rossi said.

Radić Rossi said the aim is to continue with the research in cooperation with Croatia's Ministry of Culture: “We must protect it for the future.”