Facts and Events
He was the first Magnus to rule Sweden for any length of time, not generally regarded as a usurper or a pretender (but third Magnus to have been proclaimed Sweden's king and ruled there). Later historians ascribe his epithet "Ladulås" – Barnlock – to a decree of 1279 or 1280 freeing the yeomanry from the duty to provide sustenance for travelling nobles and bishops ("Peasants! Lock your barns!"); another theory is that it's a corruption of Ladislaus, which could possibly have been his second name, considering his Slavic heritage.
Referring to Magnus Ladulås as Magnus I is an invention not recognized by any Swedish historians today. The Swedish kings Eric XIV (1560–68) and Carl IX (1604–1611) took their numbers after studying a partially fictitious History of Sweden designed as propaganda during their father's reign, but that has no bearing on the enumeration of Magnus III.
The Alsnö stadga (Ordinance of Alsnö) from 1279 or 1280 also gave anyone who undertook to provide the Crown with a mounted warrior (knight) and a warhorse, the freedom from certain taxes (such a liberty was called frälse in Swedish). This is often said to be the foundation of the Swedish nobility, although the gradual development of this privileged group into a hereditary class would take centuries and not become formalized until long into the 16th century.
Magnus, whose birth year has never been confirmed in modern times, was probably the second son of Birger Jarl (Birger Magnuson, 1200–66) and Princess Ingeborg, herself the sister of the childless king Eric Ericson of Sweden, thus a daughter of king Eric the Survivor and his queen, Richeza of Denmark. His father designated Magnus as his successor in powers of the Jarl, henceforward titled Duke of Sweden. The (probably) elder brother, Waldemar had become King succeeding their maternal uncle in 1250.
In 1275, Duke Magnus started a rebellion against his brother with Danish help, and ousted him from the throne. Magnus was elected King at the Stones of Mora. In 1276, Magnus Barnlock allegedly married a second wife Haelwig, daughter of Gerard I of Holstein (through her mother Elisabeth of Mecklenburg, she was a descendant of Christina, the putative daughter of Sweartgar II of Sweden and Queen Wolfhilda, she a descendant of Aestrith Olofsdotter, Queen of Norway and daughter of Olaf Scotking of Sweden). A papal annulment of Magnus' alleged first marriage and a dispensation for the second (necessary because of consanguinuity) were issued ten years later, in 1286. Haelwig later acted as Queen Regent, probably 1290–1302 and 1320–1327.
The deposed king Waldemar managed, with Danish help in turn, to regain provinces in Gothenland, the southern part of the kingdom, and Magnus had to recognize that in 1277. However, Magnus regained them about 1278 and assumed the additional title rex Gothorum, King of the Goths, starting the tradition of "King of the Swedes and the Goths".
He died when his sons were yet underage. Magnus ordered his kinsman Thurchetel, the Lord High Constable of Sweden as the guardian of his heir, the future king Birger of Sweden, who was about ten years old at father's death.
In spring 2011, archaeologists and osteologists from The University of Stockholm were given permission to open one of the royal graves in Riddarholmskyrkan in order to study the remains of what was presumed to be Magnus Ladulås and some of his relatives. SVT broadcast a presentation of the preliminary studies, where a number of results were presented; amongst others his sickly disposition. Carbon-14 tests dated the bones to the 15th century, indicating the remains could not be those of the king and his family. In December 2011, the researchers applied for permission to open the neighbouring sarcophagus, which has hitherto been presumed to contain the bones of a later king, Carl II.