in
the principal portal of the Church of Santa Croce in Jerusalemme are
remarkably fine specimens of it, probably taken from the Villa of
Heliogabalus, in whose gardens, called the Horti Variani, the church
was built.

Another species is the _bianco e nero antico_, the _Marmor
Proconnesium_ of antiquity, obtained from the celebrated quarries of
Proconnesos, an island in the western part of the Propontis. Many of
the towns of Greece were decorated with this marble. The internal part
of the famous sepulchre erected by Artemisia, the widow of Mausolus,
king of Caria, to her husband, and after whom all grand tombs ever
since have received the name of mausoleum, was built of this marble.
So celebrated were the quarries of Proconnesos that the ancient name
of the island was changed to Marmora, and the whole of the Propontis
is now called the Sea of Marmora. Although so highly esteemed in
Greece, this marble does not seem to have been extensively used in
Rome; the finest relics being the four columns supporting the marble
canopy, in the form of a Gothic temple, which surmounts the high altar
of St. Caecilia, which is among the most ancient of all the churches of
Rome. They were probably derived from some old Roman palace, and are
remarkable for the clearness and brilliancy of the white blotches on a
black ground. There are different varieties of this marble: one kind
in which the blotches or veins are pure black on a pure white ground,
and another in which the blotches or veins are pure white on a black
ground. In these varieties, however, the black and the white are more
confused together, but remain notwithstanding distinct and separate,
so that if the veins are white the ground is sure to be black, and
_vice versa_. The ancient _Marmor Rhodium_, or the _giallo e nero_,
had golden-coloured veins on a black ground, and, owing to its compact
texture, was capable of receiving a high polish. It is very like the
celebrated marble of Portovenere, a modern Italian species obtained
from the western hills of the Gulf of Spezia, where the formation
passes into that of the ammonitiferous limestones of the Lias and of
the palaeozoic rocks. A beautiful highly-polished specimen of Rhodian
marble exists in the mask in front of the tomb of Paul III. in the
tribune of St. Peter's, sculptured by Della Porta in 1547, long
previous to the discovery of the quarries of Portovenere. It may be
remarked that the grain of the latter species is such