'A single example might suffice to underline Grierson's inspired use of numismatic evidence dramatically to resolve a major historical controversy. This was that which raged over the historian Henri Pirenne's long-standing explanation of the survival of gold coinage in the west until the early 9th century and its replacement by silver for the next 500 years. For Pirenne, the disappearance of gold was the last act of the decline of Rome in the west, and its cause was the depredations of Islam. In 1960, Grierson published a recondite article on the monetary reforms of Caliph Abd al Malik and their financial consequences, which showed that they included a decisive shift in the relative value of silver and gold in the Islamic world, bringing about the flight of silver to the west and gold to the east. In doing so, he illuminated a major factor in the rise of monometallism that endured for five centuries in western Christendom.
Such work demanded a rare combination of skills involving mathematics, statistics, metallurgical analysis and an enviable range of languages and detailed historical knowledge. With such skills, Grierson could bring professional rigour to a world well supplied with enthusiastic amateurs, and an impressively wide range and perspective to a subject all too often studied on local lines. His scholarship gave rise, among much else, to the five volumes published by Dumbarton Oaks, and the 15 volumes planned for the Fitzwilliam Collection. These books justified his international reputation.' Neil McKendrick, obituary, The Guardian, 17th January, 2006. Full text here.
A brief 2005 video interview with Philip Grierson can be found online here. (The full DVD version available from the Fitzwilliam itself.)
The Museum's own appreciation of him - well worth reading - is downloadable here.