Through any era the extremely wealthy like to use their riches for extravagant displays of consumption.
In current times, people will pay huge amounts of money for exotic food stuffs. In China, Nests of the swiflet can fetch huge prices. The birds normally nest in remote cliffs and cave walls and make the nests with their saliva. Once the nests are taken, often with much difficulty, they are sold to be boiled in soups or made into desserts. [ref] https://www.hindustantimes.com/more-lifestyle/here-s-why-edible-nests-made-of-bird-spit-are-a-delicacy-in-china/story-bZlT6jLlGlV0TGcELzF9pI.html [/ref]
Meanwhile, caviar is synonymous as a food stuff for the ridiculously wealthy. People will pay thousands for the roe (fish eggs) of the Beluga Sturgeon, so much so that it has driven the species to near extinction. [ref] https://www.theguardian.com/food/2019/oct/16/why-is-caviar-still-on-the-menu [/ref]
In ancient Rome, the very wealthy liked to serve the tongues of exotic birds to display their status. The tongues of Flamingos, peacocks, nightingales are all recorded to have been served at banquets. The fact that only the tongue was served proved that the host was so wealthy, they didn’t need to bother with the rest of the bird. [ref] https://www.npr.org/sections/thesalt/2019/05/20/712772285/the-lavish-roman-banquet-a-calculated-display-of-debauchery-and-power https://slate.com/technology/2019/01/eat-flamingo-google-autocomplete-question.html [/ref]
But what does a Roman Emperor do to show he is the wealthiest of all? If members of the aristocracy are able to feed their guests the tongues of exotic birds, how does he upstage them?
In a crowded field of crazy emperors, Elegabalus stood out for his excess. He is said to have a saffron scented swimming pool, and one time went so far as to dump thousands and thousands of flower petals down on the heads of his guests that he nearly suffocated them. [ref] https://www.nationalgeographic.com/history/magazine/2016/03-04/elagabalus-rome/ [/ref]
So when regular aristocrats were serving exotic birds to their guests, Elagabalus promised his own guests the rarest bird of all. He is recorded as one time promising his guests a phoenix. He seemed so confident in his ability to acquire one, that should he not serve one, he would have to provide one thousand pounds of gold instead. [ref] http://penelope.uchicago.edu/Thayer/E/Roman/Texts/Historia_Augusta/Elagabalus/2*.html [/ref]
Despite all his wealth and power, it seems that failed to acquire one of the mythic birds before the main course and he dually paid out the gold instead. Sometimes all the wealth in the known world isn’t enough.
