The following is an extract from
Camden's Britannia
published in the 16th century

..... Aven being departed from hence Ringwood, entertaineth the river Stoure coming down out of Dorsetshire, where betweene the meeting of these two streames, there standeth a prety towne of trade and well peopled. At this day of a Church there dedicated unto Christ, named Christ-church: but in old time Twinamburne, because it is situate betweene the two rivers, right in the same sense that Interamna in Italie hath his name. ..... Under this towne Stoure and Aven joining together doe emptie themselves into the sea at one mouth, which Ptolomee called the mouth of the River Alaun; and rightly too: For I cannot resolve with my selfe to thinke, that the river properly was named Aven, considering this is a common name, and the Britans by that terme, called all rivers. But I would take it, that some time it was called Alaun, because there remain yet some reliques (as it were) of that name in the villages upon it, to wit, in Allington, Allingham, &c.;