ceed a few paces straight on and then descend to the right, to the
circular church of —
Santa Costanza (if closed, apply to the custodian of Sant'
Agnese, 30-50 c.), originally erected as a monument by Constantine
to his daughter Constantia, but converted into a church in 1256.
The dome, 74 ft. in diameter, is borne by twelve coupled columns
of granite. A few fragments only of the vestibule and the wall of
the original edifice now exist. In the barrel-vaulting of the am-
bulatory are blue Mosaics of the 4th cent. on a white ground,
with genii gathering grapes, birds, etc., in the antique style,
but evidently bearing traces of decline. The porphyry sarcophagus
of the saint, now in the Vatican Museum (p. 394), is similarly
adorned. The mosaics of the 7th or 8th cent. in the niches are
less interesting: Christ as the ruler of the world with apostles,
trees, and lambs. — For the Coemeterium Ostrianum, ¼ M. from
this point, see p. 455.
About 2¼ M. from the Porta Pia the road crosses the Anio
(Aniene) by the Ponte Nomentano, an ancient bridge which has
been frequently restored. It is surmounted by a medioeval tower.
Beyond the bridge, to the right, is an osteria at the foot of a hill,
which is conjectured to be the Mons Sacer rendered famous by the
Secession of the Plebs in 494 B.C. According to the story, Me-
nenius Agrippa, by the fable of the stomach and the members, here
dersuaded the Plebs to consent to a compromise, the main feature
of which was the election of the tribunes of the Plebs. Pretty view
from the top, especially from the E. edge, over the winding course
of the Anio and the pine-surrounded farm of Casale del Pazzi.
About 4 M. beyond the bridge are the Oratorio and Cata-
combs of Sant' Alessandro (p. 456).
At the Casale Capobianco, about 1 M. beyond the Oratorio a road
to the right diverges for Palombara (p. 470). — The road to the left
leads viâ Mentana (p. 109), 14 M. from Rome to (15½ M.) Monte Rotondo
(p. 109). The district is extremely bleak, but affords beautiful views of
the Sabine Mts.
d. From the Porta Maggiore.
Tramway to the Porta Maggiore, see No. 10 in the Appendix.
Two roads issue from the Porta Maggiore (Pl. II, 34; p. 213):
to the left the Via Prænestina, to the right the Via Casilina (Via
Labicana).
The ancient Via Praenestina, or Palestrina road (p. 482), to
the left, is little frequented. About 1 M. from the gate the vine-
yard-walls cease. Numerous ruins of tombs on the right indicate
the direction of the ancient route, which, lying higher, affords a
freer view than the present lower level of the road, and may be
followed by crossing the fields. About 2½ M. from the city-gate