Roman Catechism 40.9

Chapter 40 — Part IV: Prayer — The Sixth Petition: Lead Us Not into Temptation

Section 9. The Temptations Of The Devil — And besides these enemies that dwell and live with us, there are, moreover, those most bitter foes, of whom it is written: Our wrestling is not against, flesh and blood; but against principalities and powers, against the rulers of the world' of this darkness, against the spirits of wickedness in the high places. For to our inward conflicts are added the external assaults and attacks of the demons, who both assail us openly, and also insinuate themselves by stratagem into our souls, so much so that it is only with great difficulty that we can escape them.