King William and the Brecc Bennach in 1211: reliquary or holy banner?

In his Rhind Lectures of 1879 Joseph Anderson argued for identifying the Monymusk Reliquary, now in the National Museum of Scotland, with the Brecc Bennach, something whose custody was granted to Arbroath abbey by King William in 1211. In 2001 David H. Caldwell called this into question with good reason. Part of the argument relied on different interpretations of the word uexillum, ‘banner’, taken for a portable shrine by William Reeves and for a reliquary used as battle-standard by Anderson. It is argued here that none of this is relevant to the question. The Brecc Bennach is called a banner only as a guess at its long-forgotten nature in two late deeds. The word brecc, however, is used in the name of an extant reliquary, Brecc Máedóc, and Anderson was correct to think this provided a clue to the real nature of the Brecc Bennach. It was almost certainly a small portable reliquary, of unknown provenance but associated with St Columba. The king granted custody to the monks of Arbroath at a time when he was facing a rebellion in Ross, posing intriguing questions about his intentions towards this old Gaelic object of veneration.