In 829 Ansgar and his companion, Witmar, having reached Björkö (Birka), an island in Lake Mälaren and a great centre of trade, were well received and made many converts.

Late legend has it that Saint Eskil, an English bishop, disturbed a heathen sacrifice held at Strängnäs by king Blot-Sweyn and was killed.

Saint Botvid, a native layman converted in England, continued the preaching of Christianity until his murder on 28 July 1120 by a Slavonic captive whom he had redeemed.

About this time Ragnhild, wife of King Inge II, died and was buried at Södertälje, of which town she became the patron saint.

In 1176 or 1179 the new stone church at Botkyrka was consecrated by Bishop William and Stefan, Archbishop of Uppsala; the relics of Botvid were translated to it.

About this time the Cistercian nunnery of Vårfruberga (Latin: Mons Mariae) on the island of Fogdö and in 1234 the Franciscan priory at Nykoping were founded.

He built the present cathedral choir about 1481, and founded a charterhouse at Svartsjo about 1493 and a hospital for aged and infirm priests at Strängnäs in 1496.

The first two issued statutes on matters concerning the discipline of the clergy, while the synod of 1380 threatened with various penalties those who molested the tenants of church lands.

King Christian II of Sweden gave the bishopric to Jens Andersen Beldenak, Bishop of Odense, who however returned to Denmark in April 1521.

Messenius states that the bishops elect signed a document in which they promised to go to Rome to seek papal confirmation, and thus persuaded Petrus Magni to proceed to the consecration.