To indicate a house of death during the period of exposition of the body branches of pine (picea) or cypress were planted in front of the door of the house. The cypress was used because once cut it would not regrow, and was thus considered sacred to Dis, the god of the underworld, and the Roman equivalent of Pluto (Plin. NH 16.40; 16.139; Festus-Paulus 56L s.v. 'cupressus'; Hor. Od. 2.14.23). According to Servius, the marking of the death-house was intended as a warning of possible pollution which had special relevance for rhe pontiffs. Any form of contact with or sight of a corpse was thought to entail pollution and Servius claims that the Romans took particular care to keep these priests away from the sources of trouble, so that they could continue to exercise their duties in relation to public cults (Serv. ad Aen. 3.64). Pliny, in referring to these pine and cypress branches, does not mention this pollution angle, and Servius may be providing antiquarian material.

To indicate a house of death during the period of exposition of the body
branches of pine (picea) or cypress were planted in front of the door of the
house. The cypress was used because once cut it would not regrow, and was
thus considered sacred to Dis, the god of the underworld, and the Roman
equivalent of Pluto (Plin. NH 16.40; 16.139; Festus-Paulus 56L s.v.
'cupressus'; Hor. Od. 2.14.23). According to Servius, the marking of the
death-house was intended as a warning of possible pollution which had
special relevance for rhe pontiffs. Any form of contact with or sight of a
corpse was thought to entail pollution and Servius claims that the Romans
took particular care to keep these priests away from the sources of trouble, so
that they could continue to exercise their duties in relation to public cults
(Serv. ad Aen. 3.64). Pliny, in referring to these pine and cypress branches,
does not mention this pollution angle, and Servius may be providing antiquarian
material.