The history of Welzheim reaches back to the time of the Roman Empire. Around the year 160 AD the Romans founded a colony and two forts there; linguists reconstructed their Latin name as (Castra) Valentia on the base of the town's medieval name Wallenzin first mentioned in 1181. In 1980, for the 800th anniversary of the founding of the city, the eastern part (Ostkastell) of the ruins was reconstructed, and in 1993 an archeological park was founded on the site. It contains replicas of Roman stone monuments and explanatory plaques about Roman Welzheim. The western part of the fort was built over through the years.
Duino Castle was built by the Wallsee family in 1389 on the cliffs overlooking the Gulf of Trieste. It replaced an older castle from the 11th century. Over time, the Wallsee family disappeared and the castle, after having been used as a prison, became the residence of the Luogar and Hofer.
At the end of the 19th century it became the property of Prince Alexander von Thurn und Taxis from the Czech branch of the House of Thurn and Taxis. It remains with the family to this day with his great-grandson Prince Carlo Alessandro della Torre e Tasso, Duke of Castel Duino the current owner. The castle has been opened to the public as a museum and park.