A Papal Bull is a public letter or pronouncement issued by the Pope, and normally has the effect of Church Law. The term "bull" comes from the Latin bulla, meaning "seal," as they were and are issued under the Pope's seal. It is from this word that the modern term "bulletin" originates. They are still in use, although only for exceptionally solemn or formal occasions. Bulls are written in Latin, and normally are identified by the opening lines; for example, the famous Unam Sanctum ("the One Holy) issued by Boniface VIII in 1302 which asserted supreme authority of the church in all temporal matters. Another example is Ubi Pereculum (where there is danger) issued by Gregory X which established the election of Pope by a conclave of Cardinals. A more recent bull, Humanae Vitae (human life) by Pope Paul VI in 1965 condemned birth control. Papal Bulls have been extant since 500 C.E., and originally represented any letter or communication from the Pope; more recently, they are used only for solemn events such as canonization or excommunication. The link below is a list of varous Papal Bulls.