It is assumed, that he was installed as the bishop during the so-called Second Swedish Crusade around 1249 and was not only religious, but also the secular leader of the conquered Finland.

According to the older Chronicon, Bero was the first bishop to be buried in Räntämäki, apparently in Koroinen, the semi-fortified episcopal residence near Turku along the Aura river.

[4] Archaeological excavations have revealed three episcopal graves from the church ruins, rather certainly belonging to Bero and his two successors that were all claimed to have been buried there.

The modest cathedral in Koroinen, entirely made of wood at the time of Bero, was dedicated to Saint Mary, like the previous see in Nousiainen.

In addition to Koroinen, there were larger Swedish garrisons four kilometers along the Aura river inland, later known as the "Old Castle of Lieto".