Title: Gregorian calendar.
Question: What does duel dating use to show the date?

Title: Classical music.
Question: What type of instrument appears occasionally in the 20th and 21st century styles of classical music?

Title: Crimean War.
Question: Who wanted to ruled over the 12 million Orthodox Christians in the Empire?

Title: Religion in ancient Rome.
Question:
To what did the Christian church equate the peace of the emperors?