The construction materials came from an unlikely source. During the 1609 clashes, Norwegians had captured and dismantled a church that the Swedes had built in Alta, and it was this salvaged timber -- logs about ten ells in length -- that formed the bones of Altenhus Fortress. Fourteen laborers began construction in early May 1611 and finished by mid-August. Every carpenter and skilled worker had to be brought from Helgeland, far to the south, because Finnmark had none. The completed fortification was a two-story, cross-shaped blockhouse with loopholes for observation and defensive fire. Earthen ramparts surrounded three sides, while a wooden palisade guarded the fourth side facing the sea. The building of the fortress drew a wave of Norwegian settlers to an area that had been predominantly Sami, many arriving as carpenters and soldiers.

Positioned midway in the Altafjord, Altenhus could control shipping from both the north and south. Swedish spies assessed the fortification and described it as "hard to bypass." A gun-armed galley was stationed at the fortress to extend Dano-Norwegian control over the fjord's waters. The garrison's commander bore the name Thomas Koningham -- alternatively spelled Coningham or Cunningham -- suggesting a Scots or British origin not uncommon among military men in Scandinavian service. The garrison also kept two horses, likely the first horses ever brought to Alta. But this military chapter was brief. When the Kalmar War ended in 1613, Sweden abandoned its claims to the coastal territory between Tysfjorden and the Varanger Peninsula. The fortress lost its strategic purpose overnight.

After 1613, Altenhus found a grimmer use as a prison. Arrested individuals were held in the blockhouse until they could be transported to the ting -- the regional assembly court -- at Hasvag on the island of Soroya. Without maintenance, the former fortress decayed steadily, its rooms stripped of nearly all furniture and goods. Among those imprisoned were two Sami men accused in 1624 of stealing silver. Their defense was extraordinary: they claimed to have killed another Sami named Sarfe Finn, who they alleged had been plotting a rebellion against the Dano-Norwegian authorities, planning assassinations of prominent Norwegians on Aroya, at Hammerfest, Hasvag, and Sorvaer. The court was unmoved. Both men were sentenced to death for theft. The story captures the precarious position of the Sami population -- caught between competing colonial powers, subject to laws written by outsiders, and punished under a justice system that had little interest in their perspective.

In 1692, the blockhouse's remaining timber was dismantled and reused to build a church -- the fortress's final act of transformation, from Swedish church timber to Dano-Norwegian fortress to prison to house of worship. But the earthen ramparts proved more durable than any of the wooden structures they once protected. As of the early 2000s, they remain visible on Aroya, declared protected by the Norwegian Directorate for Cultural Heritage. These ramparts are the oldest surviving physical evidence of Denmark-Norway's efforts to assert control over Finnmark. The island sits quietly in the Altafjord today, its military and carceral history legible only to those who know where to look -- and what those low earthen mounds once meant for the sovereignty of salmon and the fate of nations.