In the Krakau Domschatz is a golden processional cross (the Artus Kreuz), around a wooden core, on which are mounted the fragments of two crowns of the second third of the thirteenth century (1230–60), which produce a distinctive pointed outline on the two cross arms. Their complex iconographic programme indicates that they were secular, rather than religious, objects. This programme derives from the first Arthurian romance in German – called Erec – by Hartmanns von Ave. The crowns therefore present the earliest known setting of any medieval romance in medieval applied art.

The cross, part of the ornamenta ecclesiae Poloniae, first mentioned in an inventory of 1563, was given by Casimir iii, King of Poland (1310–70), and restored by Sigismund i (1467–1548) to the cathedral. Dr Joanna Mühlemann provides an exhaustive and beautifully illustrated study of the structure of the cross and the crowns, which consist of sections of square pyramidally set stones with openwork borders, in which small figures of knights, ladies, horsemen and stags cavort. The upper part is formed of pointed openwork, the larger points set with stones and eagles with outstretched wings in the openwork.

She analyses, in great depth, the descriptions in the inventories since 1563 and the development of the understanding of the cross from the initial phase, in the mid-nineteenth century, as a national relic, to the early twentieth-century stylistic studies that related the niello and openwork to Hugo d’Oignies, to the international interest of the mid-twentieth century (the detailed analyses of Lotte Kurras in 1963 and the arguments of Joseph Deér, pointing to an Eastern, as opposed to a Western, origin), to the suggestion by Ranier Sachs that the crowns incorporated elements of an Arthurian romance (which he identified as either ‘Erec and Enide’ of Chretien de Troyes (c 1135–83) or ‘Erec’ of Hartmanns von Ave (c 1168–1210)), to the analysis of Jerzy Pietrusinki (1996) that brings in the contribution of the brooch found in the Neumarkt hoard (Środa Śląska, Poland) into play. It is one of the most impressive analyses of the changes in interpretation of a medieval object in the past 150 years.

But Mühlemann does much more than that. By detailed analyses of all the comparable works, notably the breast jewel of the Empress Constance (d. 1222) (Palermo), the crown on the bust of St Sigismund in Plock Cathedral, the Schaffhausen Onyx, the crown of the Elizabeth reliquary (Stockholm), the foot of the cross of St Atto (Pistoia), the reliquary from the former abbey of Charroux, the crystal jug from Stará Boleslav (Prague), the foot decoration of the ampulla from the Lambertikirche (Düsseldorf), the so-called Thorn Reliquary (St Mark’s, Venice), the processional cross from the Cistercian abbey of Tennenbach, as well as brooches from Darmstadt and the Essen Madonna, the Motala brooch (Stockholm), the central part of the Neumarkt/Środa Śląska brooch, together with brooches and buckles from the Victoria and Albert Museum, the British Museum and Stockholm, she is able to confirm the dating of the crowns to the period 1230–60. Further, by a close analysis of the type of the gold wirework, she is able to define a type of openwork, ‘a jour’, distinct from the work of Hugo d’Oignies and the Meuse school. It may be connected with the court of the Emperor Frederick ii, and so sets the romance and the crowns in that circle. The identifications of the figures in the romance are brilliantly shown in small photographs of details. No doubt the precision of such identifications may be disputed in the future, but this is one of the most important works of the history of thirteenth-century goldsmiths’ work to appear. Dr Mühlemann and her publisher are to be congratulated on producing such a thorough, convincing and beautifully illustrated work.