In 1788, when he was thirteen, another family friend, aware of the young man's natural ability, took him to see Major O. Wallenstjerna at Sveaborg (). Sveaborg was a Swedish fortress built on six islands just off the coast of Helsinki. The educated officers of the fort had significant influence on the culture and politics of the city. Wallenstjerna, impressed with Crusell's playing, recruited him as a volunteer member of the Sveaborg military band and gave him a place to live with his own family. Crusell received an education at Sveaborg and excelled in music and languages. In 1791 Wallenstjerna transferred to Stockholm and Crusell went with him. Although Crusell spent most of the rest of his life in Sweden, he always considered himself a Finn. In his final years in a letter to Runeberg he called himself a "finsk landsman" (a Finn). He also maintained his travel diaries in Finnish.