What is probably not so well known: Remains of stilt houses, stone coffins, flint weapons, pottery, Roman coins and jewelery were also found here.
In the 7th century, a Carolingian tufa church was built on the island. The west wall and the foundations are still preserved.
From 1545, the island changed a few times the owner and was always private property. Until 1978, the Free State of Bavaria acquired the neglected Roseninsel for 800,000 DM from the Wittelsbacher Ausgleichsfonds and made it accessible to the public again.
And Roseninsel is the only island in Lake Starnberg.