Leviticus 21:1

Speak unto the priests the sons of Aaron A quite unusual formula, not occurring elsewhere in the Pentateuch.

defile himself for the dead The defilement caused by touching a dead body lasted for seven days, and required purification by the water in which the ashes of the red heifer have been mixed, Numbers 19:11-20 (P).

The Romans (Serv ad Aen. vi. 176) used to set up a branch of cypress in front of a house containing a dead body, lest one of the pontifices should inadvertently enter and so contract pollution.