The Aristias rallied to the cause of Greek nationalism shortly before the Greek uprising of 1821. Costache joined Alexander Ypsilantis's secret society, the Filiki Eteria, which engineered the nationalist expedition in Moldavia and Wallachia. Aristia awaited the Eterists in Bucharest, which had been occupied by troops loyal to Tudor Vladimirescu, who led a parallel uprising of Romanians. In mid March, Greeks in Bucharest, led by Giorgakis Olympios, pledged to support Ypsilantis rather than Vladimirescu. The event was marked by a large display of Greek nationalism in downtown Bucharest, the details of which were committed to writing by Constantin D. Aricescu from his interview with Aristia. The actor carried the "flag of liberty", an Eterist symbol showing Constantine the Great and Helena, alongside a cross and the slogan "In this, conquer"; the obverse showed a phoenix rising from its ashes. The ceremony ended with the banner being planted on the Bellu gate, announced to the crowds as prefiguring the future reconquest of Byzantium. Reportedly, "the flag that was carried by Mr. Aristia" was later also adopted by Sava Fochianos, who deserted to Ypsilantis' Sacred Band alongside the Bucharest garrison.