marble, called sedia forata, found near the Church of St. John Lateran, upon which, in the middle ages, the Popes were obliged to sit at their installation in the presence of the Cardinals.  This custom, which was practised as late as the coronation of Julius II. in 1503, arose from a desire to secure the throne of St. Peter from being intruded upon by a second Pope Joan—­whether there ever really was such a personage, or whatever gave rise to the curious myth.  The chair is like an ordinary library chair, with solid back and sides, sculptured out of a single block, and perforated in the seat with a circular aperture. Rosso antico is not what might strictly be called a beautiful marble.  Its colour is dusky and opaque, resembling that of a bullock’s liver, marked with numerous black reticulations, so minute and faint as to be hardly visible.  But the grain is extremely fine, admitting of the highest polish.

Of black marbles—­in the formation of which both the animal and vegetable kingdoms have taken part, their substance being composed of the finely-ground remains of foraminifera, corals, and shells, and their colour produced by the carbonaceous deposits of ancient forests—­few kinds seem to have been used by the ancient Romans.  The nero antico was the species most esteemed, on account of its compact texture, fine grain, and deep black colour, marked occasionally with minute white short straight lines, always broken and interrupted.  It is the Marmor Taenarium of the ancients, quarried in the Taenarian peninsula, which forms the most southerly point in Europe, now called Cape Matapan.  The celebrated quarries which Pliny eloquently describes, but for which Colonel Leake inquired in vain, were under the protection of Poseidon, whose temple was at the extremity of the peninsula.  They attracted, on account of the sanctuary which the temple afforded, large numbers of criminals who fled from the pursuit of justice, and who readily found work in them.  Very fine specimens of this marble may be seen in a pair of columns in the obscure Church of Santa Maria Regini Coeli, near the Convent of St. Onofrio, on the other side of the Tiber; in a pair in the church of Ara Coeli; and also in a pair in the third room of the Villa Pamphili Doria, which are extremely fine, and are probably as large as any to be met with.  In consequence of the quantity used in the inscriptional tablets of monuments, for which this seems to be the favourite material, nero antico is extremely scarce in modern Rome.  The bigio antico is a grayish marble, composed of white and black, sometimes in distinct stripes or waves, and sometimes mingled confusedly together.  It was the Marmor Batthium of the ancients, and two of the large columns 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.