SUPPORTING INFORMATION S1 Archaeological context Birka was the first Viking Age town in Eastern Scandinavia and constitutes one of the most well-known archaeological sites in Northern Europe. Situated on the small island of Björkö in Lake Mälaren, now in the backwaters of Stockholm, it was once on the crossroads of communication in Eastern Central Sweden. Established in the mid-8th century, Birka quickly developed into a major centre of crafts and trade, both in the surrounding region and beyond. Throughout the following century (750 – 860 CE), Birka was part of a social and economic network centred round the coastline of the Baltic that included other urban settlements like Dorestad in the Netherlands, Ribe in Denmark, Haithabu in Germany and Truso in Poland (Sindbæk, 2007). In the latter part of the 9th century, the significance of these connections declined as Birka became an important node in the Eastern trade network sharing close contacts with similar sites in Ancient Rus’, with Byzantine metropolis Constantinople and even people of the Eurasian steppes. Specialised workshops produced jewellery, textiles and other valuables, that together with slaves were possible to trade for silver and prestigious and exotic goods (Ambrosiani, 2013; Androshchuk, 2013; Hedenstierna-Jonson, 2014). The inhabitants of the town were buried in extensive cemeteries encircling the urban area. Approximately 3000 graves have been identified within these cemeteries, and a little more than 1100 have been archaeologically examined. Most of the excavations took place in the late 19th century and the results were published in the 1940s (Arbman, 1941). Diverse mortuary practices reflect a heterogeneous population and include cremations following the regional tradition but also various forms of inhumation (Gräslund, 1980). The graves exhibit a great diversity in external and internal construction as well as in grave goods and handling of the body. This diversity reflects not only temporal trends but also a variation in socio-cultural backgrounds of the deceased. There are also differences in the spatial distribution within and between the burial grounds (Gräslund, 1980; Kalmring, 2012). The outer regions of the largest grave field, Hemlanden, and the burial grounds, South of Borg, contain cremations. The inhumations, including the chamber-graves, were situated in close proximity to the settlement-area, inside or just outside the town rampart and in the topographically 1 distinguished burial ground North of Borg. They can be considered to represent the urban population and its changes over time. Grave Bj 581 (Swedish History Museum, inventory number SHM 34000: Bj 581) was situated in a cemetery north of the hill-fort. The burials, often in coffins and sometimes in chambers, were placed on a natural terrace just outside the main entrance of the fortified area. A space empty of graves leading up to the gate and down to the garrison, marked a lane that connected these. The grave was placed at the very edge of the burial ground overlooking the water (Arbman, 1941; Gräslund, 1980). The fact that the chamber-grave was placed in a vantage point overseeing Birka’s dense center and the Viking Age royal manor at Adelsö indicates the prominence of the buried individual. Furthermore, other burials with extensive grave goods are located in the vicinity. In direct proximity to grave Bj 581 there were graves of men, women and children, all of which were richly furnished. For example, the adjacent male grave (Bj 495) (Arbman, 1941) contained amongst other things a spear, axe, shield and a ringed pin in addition to a fragment of an Arabic coin from the early 900s. In a similar type of liminal position with a landscape viewshed as the female warrior in Bj 581, was yet another weapon burial (Bj 496) (Arbman, 1941); an individual buried with shield, spear, sword, and osteologically-determined as a possible male, 25–30 years of age. The grave goods included stirrups and horse equipment, and although a platform for a horse had been built, no remains of horse bones were found in the chamber, nor were there traces of a gaming set (Figure S1.1a-b). An Arabic silver coin from 900 CE, as well as the objects, indicates that this male warrior was probably contemporary with the female warrior in Bj 581 (Arbman, 1941), but that he presumably was lower in rank. Other Scandinavian female warriors Two Viking Age burials found in southeastern and mid-Norway have been osteologically interpreted as containing young females, but have nevertheless been equipped as if they were warriors. The skeletal remains (Unimus C 22541) (Unimus, 2016) of a slender and petite woman were found in 1900 in a large burial mound located about 1.5 km east of Åsnes church in Hedmark, Norway (Hernæs, 1984). The woman had been buried, east-west oriented, around 950 CE as a fully equipped warrior, with a double-edged sword, an axe, a spear, five arrowheads, a shield, bridles, fragments of a whetstone and probably a file. At her feet lay a horse. The sword lay along the body's left side, but in reverse direction, so that its point was at the woman's head. The osteological analysis of the skeleton showed the interred to be a young 2 female, approx. 18 – 20 years of age (Holck, 1984). It has been argued that despite her outfit, the slender young woman's hand could never have been large enough to reach around the grip of the sword and thus she would have been unable to handle the sword in real combat (Hernæs, 1984), but this must be open to question. The second female Viking weapon burial seems to have lacked any marker above ground and was found at Aunvollen, close to Snåsavattnet in Nord-Trøndelag (Unimus T 20248) (Unimus, 2016). The grave goods had a conventionally all-male character and consisted of a sword, nine gaming pieces, a sickle, a whetstone, a pair of scissors, a knife and a comb. The osteological analysis showed that the female was c. 20 years old. She was accompanied by a dog. The sword scabbard was made of willow and lined with pelt, there were traces of textiles and down feathers in the grave as well. By her head (oriented towards the south) lay gaming pieces, a whetstone, a comb, scissors and some nails. The sword and sickle were probably placed by her left hip. At a later date a spear and a bead, as well as several nails or rivets were found at the site (Stenvik, 2005). S2 Osteological analyses The buried individual from Bj581 has been interpreted as being buried seated due to the position of the skeleton shown in the illustration by the excavator, Hjalmar Stolpe, where the individual was laying on the right side with the legs slightly bent. The seated posture was originally suggested by Stolpe (Stolpe, 1889), though ignored by subsequent scholars; we are the first to restore this interpretation (Figure S1.1a). Osteologist Berit Vilkans noted already in the beginning of the 1970s that the skeletal remains in the grave exhibited female characteristics (Vilkans, 1975). However, due to the fact that some finds and osteological materials from Birka have lost their contextual providence during the years of storage, Vilkans’ observations were never commented upon. Nevertheless, except for the missing cranium, the documented remains correspond with the documentation by Stolpe from 1889 (Stolpe, 1889). For example, among the depicted inhumation graves (chamber graves or coffin burials) few seem to have had complete preserved spines when excavated. During the osteological investigation, of at least 245 analysed uncremated skeletons, only four, except for Bj 581, have a complete vertebral column preserved. All bone elements have at one time been marked with the text “Bj 581” in ink. Furthermore they all 3 share the same character and colour on the surface, signifying that they were part of the same individual. S3 Archaeological sex assessment In archaeology, grave goods are often used when assessing the sex of the interred (Petré, 1984; Rundkvist, 2003). Even when there is no remaining skeletal material, the sex or gender of the individual has been determined based on artefactual evidence, though there is clearly a need for caution in such assumptions (Back Danielsson, 2007). As the bias of artefactual sex assessment is unknown, the need for osteological analyses has been stressed, but also the possibility of genetic sex determination (Conkey and Spector, 1984). S4 Genetic analyses DNA Extraction and sequencing All laboratory procedures were carried out at facilities designated solely to ancient DNA (aDNA) analyses, located at the Archaeological Research Laboratory (AFL), Stockholm University. DNA was extracted from 85 and 119 mg of bone powder from the left canine and the left humerus respectively (Table S4.1). The surface of the samples was cleaned with either 1% NaOCl (canine) or it was mechanically removed with sandpaper (humerus). Cleaned samples underwent UV irradiation at 265nm, 1J/cm2 on each side. Both samples were powdered using dentistry drills and a Dremel®4000 drill. The extraction procedure consisted of overnight digestion (buffer 0.5M EDTA pH 8, 1M Urea, 100 µg/mL Proteinase K) combined with silica-based spin column purification – MinElute PCR Purification Kit (Qiagen), according to the manufactures protocols (Malmström et al., 2009; Yang et al., 1998). Finally, DNA was eluted in 110 μl EB buffer and stored at -20oC. Of each obtained DNA extract, 20 μl were used for preparation of blunt-end Illumina genomic libraries (Meyer and Kircher, 2010). The libraries were inspected on 1% agarose gel (0.5x TBE, stained with GelRed™ x10000, Biotium Inc.) and were then amplified with AmpliTaq® Gold DNA Polymerase (Applied Biosystems™) in six separate PCR reactions with different number of cycles for the bone (x14) and the canine (x16) extracts respectively.