Porphyry. A hard stone much used in Egyptian sculpture, and for sarcophagi. It was of a fine red colour, passing into purple and green, and susceptible of a fine polish. (See also Rosso Antico.)
Porporino, It. A yellow powder substituted for gold by mediæval artists. It was compounded of quicksilver, sulphur, and tin.
Fig. 557. Porta (Gate of Perusium).
Porta, R. This term denotes the gate of a city, a large gate in any enclosure, in contradistinction to Janua and Ostium (q.v.), which denote the doors of a building. Fig. [557] shows the ancient gate of Perugia.
Portcullis. A kind of iron grating, forming an outer door, which slided up and down perpendicularly in the grooves of a bay. It was suspended by a chain, which could instantly be lowered, as occasion required, in order to prevent ingress and cut off all communication. By the Greeks and Romans they were called portæ cataractæ, and in the Middle Ages they were known as Saracenic gates.
Fig. 558. Portcullis.
Portcullis, Her. A defence for a gateway, borne as a badge by the Houses of Beaufort and Tudor. Motto, “Altera securitas.” (Fig. [558].)
Porticus, Portico, R. (porta). A long colonnade serving as a covered promenade. In an amphitheatre, the covered gallery at the top which was appropriated to women or slaves. A wooden gallery covered over with a roof, but in some cases entirely open on the side of the country. (See Templum.)