Question: The Northumbrian Dialect was spoken in a kingdom whose name reflects what approximate southern limit to the kingdom's territory?

Related documents: [0]  [DOC] The Kingdom of Northumbria ( ; Old English: "Norþhymbra rīce" , "kingdom of the Northumbrians") was a medieval Anglian kingdom in what is now northern England and south-east Scotland, which subsequently became an earldom in a unified English kingdom. The name reflects the approximate southern limit to the kingdom's territory, the Humber estuary. [END] 
[1]  [DOC] Northumbrian was a dialect of Old English spoken in the Anglian Kingdom of Northumbria. Together with Mercian, Kentish and West Saxon, it forms one of the sub-categories of Old English devised and employed by modern scholars. [END]  
Answer: the Humber estuary
the Humber estuary