Complex sentence: Other altars were donated to the churches of Leka, Røst, Hadsel, and Ørsta--the five altars are referred to by art historians as the "Leka group".
Split into simpler sentences: Other altars were donated to the churches of Leka, Røst, Hadsel, and Ørsta. The five altars are referred to by art historians as the "Leka group".