Complex sentence: The collection of Trondheim Kunstmuseum was established in 1864, and at the time named "Det Faste Galleri" (The Permanent Gallery), a name used until 1973.
Split into simpler sentences: The collection of Trondheim Kunstmuseum was established in 1864. At that time it was known as "Det Faste Galleri" (The Permanent Gallery), a name that was used until 1973.