The bishop wears an omophorion, which is more similar to the ancient pallium in shape and style than either the stole or the epitrachelion. Since the 16th century, the bishop has used a dalmatic known as the sakkos in place of the phelonion. This garment is also called a chasuble because it covers all other garments when the priest performs mass. In addition to these sacred vestments, the bishop will usually have a palace where he can live while in town. This is not necessary for priests who serve a single church (although it does help if they want to get married or have families). Finally, there is the hat worn by bishops when celebrating mass or preaching. This is the tiara, which resembles a small crown. It is made of gold or silver and is attached to the head by a chain or rope so that it cannot be lost. Bishops are always ordained priests who have been selected by their local bishop to serve as his assistant. They are usually chosen because they are known for their knowledge of church law and their ability to encourage congregations to accept the bishop's decisions peacefully. However, some bishops choose younger men because they feel that a younger priest will be more energetic or allow them to exercise control over the diocese by being seen everywhere else but at the altar during mass. It is not unusual for bishops to die suddenly.