"Wonder two: the mouth of the river Trahannon, because one wave like a mountain at The Teared [the bore] covers the banks and it ebbs like all the other seas."1,2
As a River Trannon ends the River Severn, this is likely to describe the Severn Bore (see the science page for more on this). The Severn has changed a good deal since our list was compiled - there are now weirs3
in the bore's way4. However, despite there being less obstacles then,
it is still unlikely the bore would have reached
the Trannon. The idea that the bore could filled the mighty Severn also now seems odd, however, the current weirs also
dam water higher up the river than before. Prior to this it was
shallower5, for example, at
was often a shallow stream, save where pools existed in its bed, or where a channel a few feet wide had been dredged, and held stagnant water.*
At such a place, it is easy to imagine the bore rushing up the river, overflowing the meagre channels to fill the river to the banks6. All this suggests that the Trannon is either confused with the Severn, or, that the definition of the starting point of the Trannon has changed over the years7,8,9,10,11,12.
You may like to read about the Myth and Science of this Wonder, or Visit Details for the Trannon.