Ad (BC not so much) gets nonsensical to the point of farce when talking about centuries rather than specific years. "The 20th century in the year of our lord" is utter gibberish; whereas "the 20th century of the common era" makes perfect sense.
At the age of five, Skagra decided emphatically that God did not exist. This revelation tends to make most people in the universe who have it react in one of two ways - with relief or with despair. Only Skagra responded to it by thinking, 'Wait a second. That means there's a situation vacant.'