Complex sentence: The first church known on Iceland was a post church and not a stave church, and it was built "in the north in the harbour" by Hjalte and Gissur, two of Olav Tryggvason's men.
Split into simpler sentences: The first church known on Iceland was a post church and not a stave church. It was built "in the north in the harbour" by Hjalte and Gissur, two of Olav Tryggvason's men.