The value of this dinner amounts to ten million sesterces . After consulting some references (1.2) to calculate the equivalent in euros, the dinner in question would amount to some 15 million euros . And the other question would be the number of diners, which in this case would only be one, Cleopatra VII .
Marco Antonio, Caesar's friend and her most passionate avenger, requested Cleopatra's support, which she agreed to even though her country was on the verge of ruin. After a sensual encounter in Tarsus, in her lavish royal trireme, Cleopatra demanded the execution of her sister Arsinoe as a prerequisite for helping Antony, who agreed to her proposal. On that date, both fell passionately in love. Cleopatra, trying to impress her lover, bet that she was capable of getting "between chest and back" a dinner of ten million sesterces. Logically, Marco Antonio accepted.
When the day in question arrived, dinner was served with the most exquisite and, logically, expensive delicacies (to find out what a dinner of the time can be like, you can see it here) but nothing unusual in view of Marco Antonio. Cleopatra arrived at the appointment with an impressive necklace with two beautiful pearls, she went to Planco, chosen judge of the contest, and asked him how much each one of the pearls could be worth:«At least five million sesterces «, answered the judge.
After said "appraisal", Cleopatra poured one of the pearls into a glass and filled it with vinegar (remember that pearls are mainly made up of calcium carbonate which, when reacting with vinegar, releases calcium and CO2) so that the pearl would dissolve and be able to drink it. When she was going to repeat the operation with the second pearl, to "spend" the ten million, Marco Antonio gave up.
Source:World History without the boring bits – Fernando Garcés