How were large sums of money exchanged in the early middle ages like Anglo-Saxon England when silver pennies were the only currency. And if Byzantine solidus or Arab denar gold coins were used then what were the exchange rates to silver pennies?
We have limited but important evidence in England for the use of mancuses, a gold coinage that was intended largely for symbolic use rather than economic transactions. These show up most often in wills as a sign of value rather than necessarilyas coinage, however: one will of an Ælfswith leaves 80 mancuses to Christ's Church, Canterbury, while that of a Wynflæd bequeathed 16 mancuses to her grandson 'to enlarge his beah', suggesting that it often contextualises as a weight of bullion rather than as discrete coins (a beah being a form of torque or arm ring that could function simultaneously as a gaudy display of status and a personal gold reserve). The terms are used annoyingly interchangeably: the will of King Eadred in 955 for example orders that:
nime man twentig hund mancusa goldes and gemynetige to mancusan
Or literally, that twenty hundred mancuses of gold be taken and minted into mancuses.
We only have very, very few examples of a mancus coin, the most famous of which is minted by Coenwulf of Mercia in the 820s. An earlier "mancus" of Offa is minted in the style of an Arabian dinar and appears to have used that currency as a basis for weight and value. The use of the mancus seems to have been an adoption from Northern Italy, where the dinar was in use as a golden coin, likely travelling back with Mercian delegates to the Pope. Indeed, the English issues could be interpreted as a prestige endeavor, making a version of the same coinage that is nonetheless conspicuously "English" for use in a wider European monetary system, similar to how modern-day Euros are still stamped with their country of origin.
Despite the existence of physical mancus coins, the value was almost certainly one of equivalence rather than for transactional use, the mancus being equivalent to roughly some 30 pennies. The two thousand mancuses of Eadred, for example, are likely to have been prestige gifts - trinkets almost - given as a beneficence to his thegns and ministers rather than used as a lump sum. Even in large sums, the functional currency of the Anglo-Saxons seems to have remained the erstwhile silver penny in commonplace use throughout the country. Widespread hoard evidence both domestically and abroad shows that the penny was used in bulk as well as in expected low-value transactions. Hoards from the port of Chester and Hiberno-Norse trade settlements in Ireland, for example, show that traders kept large reserves of pennies. A significant and important trove of Eadred pennies in Rome (still kept in the Vatican archive) show that even when a tribute of Mancuses was sent to the Pope, the actual currency dispatched was pennies. Similarly, large hoards of Æthelred II pennies from Scandinavia suggest that the large gafol payments of the early eleventh century were likewise paid in pennies.