In the cove Sepen, just a few kilometres by air to the south of Omišalj, there is an inexhaustible site of archaeological heritage. The first traces of settling in the area date back into the 1st century when the Roman town Fulfinum emerged. Its emergence is related to the construction of the city for the retired Roman soldiers during the Flavian dynasty. A good geographical position caused the development of seafaring and trade. The past archaeological research discovered the city forum, the heart of every city from the Roman age, the centre of the social and religious life of the Romans. Here, only fifty meters from the sea, is where the foundations of the temple, the civilian basilica and the commercial edifices (tabernae) were found. In one moment during the 3rd century, the city simply died out, at least when it comes to its original monumental form. Still, life continued. Traces of more modest settlement of the area were found, probably connected with the port which is still in function.References:
First record of Kastelholma (or Kastelholm) castle is from the year 1388 in the contract of Queen Margaret I of Denmark, where a large portion of the inheritance of Bo Jonsson Grip was given to the queen. The heyday of the castle was in the 15th and 16th centuries when it was administrated by Danish and Swedish kings and stewards of the realms. Kastelhoma was expanded and enhanced several times.
In the end of 16th century castle was owned by the previous queen Catherine Jagellon (Stenbock), an enemy of the King of Sweden Eric XIV. King Eric conquered Kastelholma in 1599 and all defending officers were taken to Turku and executed. The castle was damaged under the siege and it took 30 years to renovate it.
In 1634 Åland was joined with the County of Åbo and Björneborg and Kastelholma lost its administrative status.