But the eighth century is taken up with the greatness of Mercia.

Ecgfrith, the last great king of Northumbria, whose over-lordship extended over the Picts of Galloway and the Cumbrians of Strathclyde, endeavoured to carry his conquests beyond the Forth, and annex the free land lying to the north of the old Roman line.

He was defeated and slain, and with him fell the supremacy of Northumbria.
Mercia, which already, under Penda and Wulfhere, had risen to the second place, now assumed the first position among the Teutonic kingdoms.
Unfortunately we know little of the period of Mercian supremacy.

The West Saxon chronicle contains few notices of the rival state, and we are thrown for information chiefly on the second-hand Latin historians of the twelfth century.

AEthelbald, the first powerful Mercian king (716-755), "ravaged the land of the Northumbrians," and made Wessex acknowledge his supremacy.