Nicholas had a really busy eight years as pope, from 1447 to 1455. He spent much of it restoring Rome, which had been in a bad way since the invasions of the 700's. The fortifications were crumbling, the aqueducts hadn't worked for centuries, the Vatican and St. Peter's were in poor shape. He rebuilt all of these, and polished up the rest of the city along with it. He encouraged the growth of humanist scholarship, and was a patron of great artists like Fra Angelico.

Unlike his predecessor, Nicholas took a particularly shameful stance on slavery. In several major documents, he specifically authorized European traders to enslave any Muslim, Saracens, or 'unbelievers' into permanent slavery. The infidels got their back, somewhat, by conquering the city of Constantinople in 1453.