January 18, 802: Pope cancels short-lived Archbishopric of Lichfield (787-802)
The heartland of Mercia, shown as "Mercia" on the map, was in the west of England, the region around Lichfield and Repton and Tamworth. But in the eighth century, under kings Æthelbald (716-57) and Offa (757-96), Mercia often held control of most of the other English kingdoms south of the Humber, hence the larger legend for the "Mercian Supremacy" (see more detailed map). The apparent independence of Wessex was probably compromised when King Beorhtric of Wessex (786-802) married one of Offa's daughters, which from the time of Hengest and Vortigern (who, so the legend runs, married Hengest's daughter Rowenna) often gave the father-in-law some authority over his new son.
That the Mercian Supremacy was neither peaceful nor uncontested can be seen from the way that most of the other kingdoms rebelled at Offa's death in 796, and Kent seems to have been independent for almost ten years after a battle in 776. And the archbishop of Canterbury in Offa's day, Jænberht (765-792), seems to have had thoroughly Kentish loyalties.
This was unfortunate for Offa, because it seems that when he wanted his son Ecgfrith to be anointed king (a novel new procedure introduced by Charlemagne in 781), Jænberht refused to do it. Rather than have a protracted fight with the archbishop, as King Coenwulf of Mercia would do with Archbishop Wulfred in 816, Offa petitioned the Pope that a third archbishopric should be formed, at Lichfield in the Mercian heartlands. This was duly done in 787, and one of Archbishop Hygeberht of Lichfield's first duties was to anoint Offa's son Ecgfrith.
Ecgfrith only lived for 141 days after his father's death, and the next Mercian king, Coenwulf, set about dismantling the third archbishopric, telling the Pope that Offa had only created it out of enmity to Jænberht and Kent. But Coenwulf did suggest that a single southern archbishopric should be re-established not at Canterbury, but at London -- it had been Gregory the Great's original plan that the archbishoprics should be established at York and London, but Coenwulf would have been more motivated by the fact that London was more firmly under Mercian control. In any event, the Pope would have none of it, and wrote to Archbishop Æthelheard of Canterbury on January 18, 802, confirming the ancient privilege of his see.
For more on the machinations, see under 787.