Complex sentence: For this, Pope Alexander had a new opening created in the "portico" of St. Peter's and commissioned a marble door which lasted until 1618, when another door was installed in the new basilica.
Split into simpler sentences: For this, Pope Alexander had a new opening created in the "portico" of St. Peter's and commissioned a marble door. This door lasted until 1618, when another door was installed in the new basilica.