According to the Primary Chronicle, in the early 11th century, Anthony, an Orthodox monk from Esphigmenon Monastery on Mount Athos, originally from Liubech of the Principality of Chernihiv, returned to Rus' and settled in Kiev as a missionary of monastic tradition to Kievan Rus'. He chose a cave at the Berestov Mount that overlooked the Dnieper River and a community of disciples soon grew. Prince Iziaslav I of Kiev ceded the whole mount to the Antonite monks who founded a monastery built by architects from Constantinople. This was the Kiev Caves Lavra. Saint Theodosius' greatest achievement has been the introducing of the monastic rule of Saint Theodore the Studite in the Monastery of the Caves whence it spread to all the monasteries of the Russian Orthodox Church.
In the Orthodox Church, their names are often listed together and they are commemorated together on September 2, while each has his own feast day as well (July 10 for St. Anthony and May 3 for St. Theodosius).