thumb|Seal of King Magnus
thumb|14th-century depiction of King Magnus on a high tower wall of his burial church
thumb|Magnus's 16th century grave monument over his family crypts in [[Riddarholm Church]]
Magnus Ladulås (, ) or Magnus Birgersson ( 1240 – 18 December 1290) was King of Sweden from 1275 until his death in 1290.
He was a son of Birger Jarl, and became a king after a rebellion against his brother Valdemar. He was succeeded by his ten-year-old son Birger Magnusson with Torkel Knutsson acting as his guardian.
Medieval Swedish kings did not use regnal numbers as part of their title. In modern literature he may be referred to as either Magnus I or Magnus III.
Epithet
The origin of the epithet Ladulås () is not known for certain, due to the lack of source material from the latter half of the 14th century. It appears widely in written documents from the beginning of the 15th century, with the Visby Chronicle from 1412 being the oldest datable document. Lilla rimkrönikan from gives the traditional explanation, ascribing the epithet to the Ordinance of Alsnö. This act by Magnus freed the yeomanry from the duty to provide sustenance for travelling nobles and bishops, and "locked the barns".
Early life
thumb|left|150px|Magnus's father Birger Jarl
Magnus was born around 1240 as the second son of Birger Jarl (1200–66) and Princess Ingeborg, daughter of King Erik Knutsson and sister of King Erik Eriksson of Sweden. The early life of Magnus is poorly documented, but he seems to have received an extensive education.
When Birger died in 1266, Magnus assumed his title as the Duke of Sweden. The title was not accompanied by any unified territory, but by a number of scattered estates and rights to collect taxes and fines. He also received Nyköping Castle in Södermanland.
There is no indication that he would have received the powers of his father.
In 1276, Magnus married Helvig, daughter of Gerard I of Holstein. Through her mother, Elizabeth of Mecklenburg, Helvig was a descendant of Christina, the putative daughter of King Sverker II. A papal annulment of Magnus' alleged first marriage and a dispensation for the second (necessary because of consanguinity) were issued ten years later, in 1286. Helvig later acted as regent, probably 1290–1302 and 1320–1327.
Magnus died when his sons were yet underage. Magnus ordered his kinsman Torkel Knutsson, the Lord High Constable of Sweden as the guardian of his heir, the future King Birger, who was about ten years old at father's death.
Modern research
In spring 2011, archaeologists and osteologists from the Stockholm University were granted permission to open one of the royal tombs in the Riddarholmen Church, traditionally believed to contain the remains of Magnus Ladulås and some of his relatives. An osteological and odontological examination revealed the presence of five male and two female skeletons. Preliminary studies indicated a notable sickly disposition in one skeleton, previously presumed to belong to Magnus Ladulås based on descriptions of his ailments. Contrary to expectations, radiocarbon dating indicated that the skeletons were from the 15th and early 16th centuries, and could not belong to the king and his family.
Issue
From his alleged first (annulled) marriage to an unknown woman:
- Erik (born c. 1275 – c. 1277)
From his second marriage to Helvig of Holstein:
- Ingeborg (1277 – 1319); married King Eric VI of Denmark.
- Birger (1280 – 1321), King of Sweden from 1290 to 1318
- Erik (c. 1282 – 1318), duke, father to King Magnus Eriksson; the Erik's Chronicle is named after him
- Valdemar (after 1282 – 1318), Duke of Finland. Erik and Valdemar died of starvation 1318 at Nyköping Castle while imprisoned by his brother, King Birger.
- Rikissa (<abbr>c.</abbr> 1285 after 1347), Abbess of the convent of St. Clare's Priory, Stockholm.