You use AD in dates to indicate the number of years or centuries that have passed since the year in which Jesus Christ is believed to have been born. Compare BC.
双语例句
例： The original castle was probably built about AD 860.
原先的城堡可能是在公元860年前后修建的。
例： The cathedral was destroyed by the Great Fire of 1136 AD.
这座大教堂被公元1136年的大火烧毁了。