But the most remarkable monument of antiquity in this part is the marble triumphal Arch of Septimius Severus, which stands in front of the ruins of the Temple of Concord.  It invaded the site of the republican Graecostasis, where foreign ambassadors waited for an audience of the senate, and occupied part of the area of the Comitium, whose original character was thereby destroyed; for it was erected at a time when men ceased to care for the venerable associations connected with the early history of their city.  One gazes upon this monument of Roman power and pride with deep respect, for it has stood nearly seventeen centuries; and though rusty and sorely battered, and its sculptures much mutilated, it is still one of the most solid and perfect relics of imperial times.  It was raised to commemorate the wars of Septimius Severus in Parthia and Arabia; and represents among its carvings the goddess Rome receiving the homage of the Eastern nations.  It exhibits on its panels many scenes connected with his campaigns, the memory of which no humane man would have liked to perpetuate.  On the upper part of the Arch is a large inscription in honour of the emperor and his two sons, Caracalla and Geta.  The name of Geta, however, was afterwards erased by his brother when he had murdered him, and other words substituted.  Marks of the erasure may still be seen perfectly distinct after all these centuries, and vividly recall the terrible associations of the incident.  The dislike which Caracalla and Geta had for each other was so virulent that their father took them both with him to Britain, in order that they might forget their mutual animosity while engaged in active warfare.  Septimius Severus died during this campaign at York, and his sons returned to Rome to work out soon after the domestic tragedy of which this Arch reminds us.  On the top of the Arch there was originally a bronze group of a chariot and four horses, with the emperor and his sons driving it.  But this was removed at an early date; and in the middle ages the summit of the Arch supported the campanile of the church of St. Sergius and Bacchus that was built up against its sides.  A little to the left, the road passing under the Arch joins the Clivus Capitolinus which wound through the Forum, and led up to the great Temple of Jupiter on the Capitol.  The pavement of this ancient road, which still exists, is formed of broad hexagonal slabs of lava, and is as smooth and as finely jointed at this day as when the triumphal processions of the victorious Roman generals used to pass over it.

At the western corner of the Arch of Severus are the scanty remains of a tall conical pyramid, about fifteen feet in diameter, which is identified as the Umbilicus Romae, placed in the exact centre of old Rome.  Not far from it stood the Milliarium Aureum, or Golden Milestone, on which were inscribed all the distances of roads without the walls.  The Roman roads throughout the empire terminated at this point.  With this