"Pērkoņkalve" indicates a departure from the war themes (Battle of Saule, Latvian War of Independence, and Latvian Riflemen) covered by the band's previous albums. It is a concept album about Latvian mythology with the Latvian god of thunder Pērkons depicted on the cover, striking an anvil with his hammer. "Pērkoņkalve" goes through the ancient Latvian year and starts with a song about the arrival of spring god Ūsiņš.