Since Archbishop Matthias Rátót of Esztergom was killed by the Mongols in the Battle of Mohi, Achilles administered the archdiocese for more than two years.
King Béla IV of Hungary granted him a landed property in Ugocsa County which suggests that the monarch also respected Achilles's work.
This occurred following Daniel repulsed the attack of the Hungarians led by Béla's son-in-law and claimant Rostislav Mikhailovich in the previous year.
[5] When Bishop Bartholomew le Gros of Pécs retired in 1251, King Béla IV recommended Achilles to his place.
The new bishop visited the monastery his predecessor had established for hermits on the Saint James (Ürög) Hill at Pécs and personally marked out the borders of its nearby properties.