destroyed, including paintings, sculptures, altarpieces, stained glass, and crucifixes, and the survival rate of works by the major artists is low – even Jan van Eyck has only some 24 extant works confidently attributed to him. The number grows with later artists, but there are still anomalies; Petrus Christus is considered a major artist, but is given a smaller number of works than van Eyck. In general the later 15th-century works exported to southern Europe have a much higher survival rate. Many of the period's artworks were commissioned by clergy for their churches, with specifications for a physical format and pictorial content that would complement existing architectural and design schemes. An idea of how such church interiors might have looked can be seen from both van Eyck's Madonna in the Church and van der Weyden's Exhumation of St Hubert. According to Nash, van der Weyden's panel is an insightful look at the appearance of pre-Reformation churches, and the manner in which images were placed so that they resonated with other paintings or objects. Nash goes on to say that, "any one would necessarily be seen in relation to other images, repeating, enlarging, or diversifying the chosen themes". Because iconoclasts targeted churches and cathedrals, important information about the display of individual works has been lost, and with it, insights about the meaning of these artworks in their own time. Many other works were lost to fires or in wars; the break-up of the Valois Burgundian state made the Low Countries the cockpit of European conflict until 1945. Van der Weyden's The Justice of Trajan and Herkinbald polyptych is perhaps the most significant loss; from records it appears to have been comparable in scale and ambition to the Ghent Altarpiece. It was destroyed by French artillery during the bombardment of Brussels in 1695, and is today known only from a tapestry copy. Documentation There have been significant challenges for art historians in establishing the names of Netherlandish masters and attributing specific works. The historical record is very poor, such that some major artists' biographies are still bare outlines, while attribution is an ongoing and often contentious debate. Even the most widely accepted attributions are typically only as a result of decades of scientific and historical research originating from after the start of the 20th century. Some painters, such as Adriaen Isenbrandt and Ambrosius Benson of Bruges, who were mass-producing panels to be