Xanthos was initiated into a Freemasonic Lodge at Lefkada ("Society of Free Builders of Saint Mavra"), while Tsakalov was a founding member of the Hellenoglosso Xenodocheio (Greek: Ελληνόγλωσσο Ξενοδοχείο, meaning Greek-speaking Hotel) an earlier relative society for the liberation of Greece which had been founded in Paris and made a progress to the Greek nationalistic ideas.

[7] Massive initiations began only in 1818 and by early 1821, when the Society had expanded to almost all regions of Greece and throughout Greek communities abroad, the membership numbered in thousands.

[8] Among its members were tradesmen, clergy, Russian consuls, Ottoman officials from Phanar and revolutionary Serbs, most notably, the leader of the Serbian Revolution, father of the modern Serbia and founder of the Karadjordjevic dynasty Karageorge Petrovic.

[8][9] Members included primary instigators of the Greek revolution, notably Theodoros Kolokotronis, Odysseas Androutsos, Dimitris Plapoutas, Papaflessas and the metropolitan bishop Germanos of Patras.

[6] The team of leaders made and spread its decisions, saying that they transmitted the commands of an "Invisible Authority" (Αόρατος Αρχή), who was thought to be one or more strong persons, so that from the start it was shrouded in mystery, secrecy and glamour.

Members of the society came together in what was called a "Temple" with four levels of initiation: a) Brothers (Αδελφοποίητοι) or Vlamides (Βλάμηδες), b) the Recommended (Συστημένοι), c) the Priests (Ιερείς) and d) the Shepherds (Ποιμένες).

[11] I swear in the name of truth and justice, before the Supreme Being, to guard, by sacrificing my own life, and suffering the hardest toils, the mystery, which shall be explained to me and that I shall respond with the truth whatever I am asked.When the Priest approached a new member, it was first to make sure of his patriotism and catechize him in the aims of the society; the last stage was to put him under the lengthy principal oath, called the Great Oath (Μέγας Όρκος).

[11] Much of the essence of it was contained in its conclusion:[10] Last of all, I swear by Thee, my sacred and suffering Country,— I swear by thy long-endured tortures,— I swear by the bitter tears which for so many centuries have been shed by thy unhappy children, by my own tears which I am pouring forth at this very moment,— I swear by the future liberty of my countrymen, that I consecrate myself wholly to thee; that hence forward thou shall be the cause and object of my thoughts, thy name the guide of my actions, and thy happiness the recompense of my labours.When the above was administered the Priest then uttered the words of acceptance of the novice as a new member:[11] Before the face of the invisible and omnipresent true God, who in his essence is just, the avenger of transgression, the chastizer of evil, by the laws of the Eteria Filiki, and by the authority with which its powerful priests have intrusted me, I receive you, as I was myself received, into the bosom of the Eteria.Afterwards the initiated were considered neophyte members of the society, with all the rights and obligations of this rank.

In early 1818, they had a meeting with Ioannis Kapodistrias, who not only refused, but later wrote that he considered Filiki Eteria guilty for the havoc that was foreboded in Greece.