This was the Roman Exchange, where the money-changers transacted their
business, and must not be confounded with the Temple of Janus already
mentioned; nor must it be thought that there were a series of arches
here, as some authors have supposed. Horace says (Sat. ii. 3), "Since
all my fortunes were dissipated at the middle exchange" (Janus). Again
(Ep. i. 1), "O citizens, money is to be sought first; virtue after
riches. This is inculcated from the top to the bottom of 'change." He
here distinguishes the _summus_, _medius_, and _imus_, or the top,
middle, and bottom of the exchange.