On the left of the entrance is the descent into the catacombs, with the inscription:
"In hoc sacrosancto loco qui dicitur ad Catacumbas, ubi sepulta fuerunt sanctorum martyrum corpora 174,000 ac 46 summorum pontificium pariterque martyrum. In altare in quo corpus divi Sebastiani Christi athletæ jacet celebrans summus Pontifex S. Gregorius Magnus vidit angelum Dei candidiorem nive, sibi in tremendo sacrificio ministrantem ac dicentem, 'Hic est locus sacratissimus in quo est divina promissio et omnium peccatorum remissio, splendor et lux perpetua, sine fine lætitia, quam Christi martyr Sebastianus habere promeruit.' Prout Severanus Tom. Pº. pagina 450, ac etiam antiquissimæ lapideæ testantur tabulæ.
"Ideo in hoc insigne privilegiato altari, tam missæ cantatæ quam privatæ, dum celebrante, animæ quæ sunt in purgatorio pro quibus sacrificium offertur plenariam indulgentiam, et omnium suorum peccatorum remissionem consequuntur prout ab angelo dictum fuit et summi pontifices confirmarunt."
These are the catacombs which are most frequently visited by strangers, because they can always be seen on application to the monks attached to the church,—though they are of greatly inferior interest to those of St Calixtus.
"Though future excavations may bring to light much that is interesting in this cemetery, the small portion now accessible is, as a specimen of the Catacombs, utterly without value. Its only interest consists in its religious associations: here St. Bridget was wont to kneel, rapt in contemplation; here St. Charles Borromeo spent whole nights in prayer; and here the heart of St. Philip Neri was so inflamed with divine love as to cause his very bodily frame to be changed."—Northcote's Roman Catacombs.
"Philip, on thee the glowing ray
Of heaven came down upon thy prayer,
To melt thy heart, and burn away
All that of earthly dross was there.
"And so, on Philip when we gaze,
We see the image of his Lord;
The saint dissolves amid the blaze
Which circles round the Living Word.
"The meek, the wise, none else is here,
Dispensing light to men below;
His awful accents fill the ear,
Now keen as fire, now soft as snow."
J. H. Newman, 1850.
Owing to the desire in the early Christian Church of saving the graves of their first confessors and martyrs from desecration, almost all the catacombs were gradually blocked up, and by lapse of time their very entrances were forgotten. In the fourteenth century very few were still open. In the fifteenth century none remained except this of St. Sebastian, which continued to be frequented by pilgrims, and was called in all ancient documents "cœmeterium ad catacumbas."
At the back of the high-altar is an interesting half-subterranean building, attributed to Pope Liberius (352—355), and afterwards adorned by Pope Damasus, who briefly tells its history in one of his inscriptions, which may still be seen here: