But Vespasian’s Forum, famous as it was, and valuable as its restored plan is to illustrate archaeological inference at work, is overshadowed by his mightiest monument, which has survived to become the very symbol of pagan Rome to modern times: the Flavian Amphitheater or Coliseum. More perhaps than any other classical monument, its stones are steeped in blood and memories; in the blood of gladiators and wild beasts, and perhaps of Christian martyrs, in memories of medieval battles, Renaissance plundering of stone (much of the travertine in St. Peter’s came from it), and Victorian moonlight visits. Having resisted earthquakes, fire, and demolition, it is now menaced by the vibrations of modern traffic. Work on strengthening its walls against this new threat has been going on since 1956. For sheer mass the Coliseum deserves its name. It is a third of a mile around, and the Italian engineer G. Cozzo has calculated that 45,000 cubic meters of travertine went into its outside wall, over twice as much into the whole structure. But the achievement here is not mere massiveness, but precise engineering, careful calculations of stresses and strains, avoidance of crowding at entrances and exits, perfect visibility, ingenuity in the arrangements for getting the wild beasts into the arena. (Perhaps this is the place to recall that it was upon the Coliseum that Charles Follen McKim based his design for the Harvard Stadium.) The site chosen, the bed of the pool of Nero’s Golden House, was good propaganda and good engineering. Propaganda-wise, it made for good public relations to turn a detested Emperor’s pleasure grounds into a place for public enjoyment. (Neither Vespasian nor the Roman mob would have thought of the slaughter of men and beasts as anything but enjoyable; their attitude at best was that of Hemingway to a bullfight.) From the engineering point of view, it saved much costly excavation to pump out the pool and use it for the substructure of the arena, and in the low, soft ground, footings could go deep: eight feet of concrete under the _cavea_. Besides, the huge mass of debris from the demolished Golden House could be cannily reused in the new fabric. The first step was to erect a skeleton of travertine piers, a double row, built of squared blocks held together not with mortar but with metal clamps. The holes where these clamps were wrenched out, 300 metric tons of them, in the metal-starved Middle Ages, are visible today throughout the fabric. Differences in construction suggest that the huge project was divided into four quadrants, each assigned to a different contractor. Most of the work is honest, so that, for example, one cannot get the proverbial penknife blade into the joints between the blocks of the piers, but in the northwest quadrant the work is shoddy. This is precisely the section that has given the most trouble under the strain of the traffic vibrations of modern times.