Mail from the Garrison of Birka
A Review of Recent Research
Mail is the best attested form of body armour from early medieval Europe. Construction of mail is considered quite uniform, however it does vary in details which further research may eventually link to particular cultural origins or periods. The purpose of this article is to describe the properties of tenth century mail as known from some archaeological discoveries, in particular those at the major Viking age settlement/trading town of Birka  in Sweden.
The Garrison at Birka
Organised excavations have occurred on Björkö for more than 130 years . The site of Birka near the lake shore is marked by an occupation layer rich in organic material and artefacts called the Black Earth, which was the major focus of Hjalmar Stolpes early excavations in the nineteenth century. The town was defended by earthworks, including a hilltop fort - the Borg which was more closely examined by Holger Arbman in the 1930s. He was the first to determine that an area just outside the fort had a notable concentration of remains of military equipment. That area, now colloquially called the Birka Garrison, was the subject of intensive investigations by Lena Holmquist Olausson in the years 1998-2002. A barracks and workshop was uncovered, including a forge where mail was repaired but probably not manufactured on any significant scale.
Mail from the Garrison
About 100 finds of mail fragments have been recovered from the Garrison by the three excavations mentioned above, which are described by Fredrik Ehlton in his report . They are mostly single rings but there are thirty-eight examples where two or more rings are interlinked, including some small patches of less than a dozen links each. Of these twenty-four finds are well preserved enough to reveal their construction, and all of these are made of alternating rows of riveted and solid rings, like almost every example of mail known from the early medieval period [4, 5].
Figure 1 - Size distribution of mail rings discovered at Birka Garrison by different excavators. Data from Ehlton .
Thickness measurements of corroded wire are uncertain, however the results from twenty-four specimens which I judged to be sufficiently well preserved are shown in Figure 2 below, plotted with the external diameter of each ring. Data from two well-studied comparable finds, the aventail of the late 8th century Coppergate helmet (York, England)  and the fragmentary mail garment from the 10th century cremation grave at Gjermundbu (Buskerud, Norway)  have been included:
Figure 2 - Plot of wire thickness and external diameter of some mail ring finds discovered at Birka Garrison.
Naturally larger rings tend to be made of thicker wire - the typical ratio was about 6:1 though, as the plot makes obvious, there is a lot of variation .
To produce riveted links from wire the cut ends are overlapped and flattened, a hole is punched through the lap and it is fastened together with a small rivet. All known examples of medieval mail including those from Birka have an anticlockwise lap - if held with the lap uppermost the right-hand end would be in front of the left . At Birka the wire expands in width at the lap only to a slight to moderate degree , and there are examples of rings expanded mainly toward the outside, to the inside, and evenly (the most common). Such rivet heads as can be observed (Figure 3) are large, hemispherical and prominent . They are smoothly rounded not facetted, showing they were set with a swaging tool, not hammered directly.
Figure 3 - Mail rings from Birka Garrison . Left - three riveted links showing moderate lap expansion and the variation in size of rivet heads. Right - a solid link of round cross-section, the thickened region may be a welded scarf joint. Finds (from left) G-01A8a (11.4mm); G-981173 (11.1mm); G-981085 (11.8mm); 993777 (9.0mm).
In the literature two methods have been proposed for producing solid rings - by punching them from solid iron sheet , or producing them from wire in the same manner as the riveted ones and welding them closed . The former method should produce a squarish cross-section like a washer, and the latter a round section. The great majority of the Birka solid rings are of round section (including three that are oval), while there are only three examples that definitely have flat sections , and on this basis alone it might appear that most of them were created by welding (Figure 3, right). In practice however the distinction is not so simple, as it appears mail makers made some effort in smoothing corners off punched links  - while it would take just a simple hammer blow to the face of a round wire link to flatten it to resemble a square section.
Several characteristics should be considered when trying to authentically reproduce the appearance of mail armour based on the Birka Garrison. It should be constructed from alternating rows of riveted and solid rings, ideally both made from round section wire. Though a range of dimensions are possible, the most typical rings would be around 9 to 11mm diameter and made of 14 gauge wire. The laps would be anticlockwise and somewhat expanded to accommodate a rivet with a prominent hemispherical head.