5th October 2010, 12:53 PM
Not sure that you would want the weight of stone baring down on piles as this might cause them to differentially subside and pull apart the stonework. The planks might have been a way to form a flat base on which to distribute the stone work. That they are ashlars would suggest that they were intended to fit/lock neatly together. Possibly there are two phases (of construction if not of use) going on with an original construction based on wooden piles followed by a consolidated stone bridge.
(I make this up as I go along)
(I make this up as I go along)
Reason: your past is my past