“Of those pots you mention, there are not any remaining in the Circus Maxiouis, as the walls, seats and apodium of that have entirely disappeared.  They are to be seen in the Circus of Caracalla, on the Appian way; of this, and of this alone, enough still exists to ascertain the form, structure, and parts of a Roman course.  It was surrounded by two parallel walls which supported the seats of the spectators.  The exterior wall rose to the summit of the gallery; the interior one was much lower, terminated with the lowest rows, and formed the apodium.  This rough section may serve to elucidate my description.  From wall to wall an arch was turned which formed a quadrant, and on this the seats immediately rested:  but as the upper rows were considerably distant from the crown of the arch, it was necessary to fill the intermediate space with materials sufficiently strong to support the upper stone benches and the multitude.  Had these been of solid substance, they would have pressed prodigious and disproportionate weight on the summit of the arch, a place least able to endure it from its horizontal position.  To remedy this defect, the architect caused spherical pots to be baked; of these each formed of itself an arch sufficiently powerful to sustain its share of the incumbent weight, and the whole was rendered much less ponderous by the innumerable vacuities.

[Illustration]

“A similiar expedient was likewise used to diminish the pressure of their domes, by employing the scoriae of lava brought for that purpose from the Lipari Islands.  The numberless bubbles of this volcanic substance give it the appearance of a honeycomb, and answer the same purpose as the pots in Caracalla’s Circus, so much so, that though very hard, it is of less specific gravity than wood, and consequently floats in water.”

Before I quit the Circus of Caracalla, I must not forbear mentioning his bust, which so perfectly resembles Hogarth’s idle ’Prentice; but why should they not be alike?

    For black-guards are black-guards in every degree,

I suppose, and the people here who shew one things, always take delight to souce an Englishman’s hat upon his head, as if they thought so too.

This morning’s ramble let us to see the old grotto, sacred to Numa’s famous nymph, AEgeria, not far from Rome even now.  I wonder that it should escape being built round when Rome was so extensive as to contain the crowds which we are told were lodged in it.  That the city spread chiefly the other way, is scarce an answer.  London spreads chiefly the Marybone way perhaps, yet is much nearer to Rumford than it was fifty or sixty years ago.

The same remark may be made of the Temple of Mars without the walls, near the Porta Capena:  a rotunda it was on the road side then:  it is on the road side now, and a very little way from the gate.