Each pier was formed by driving a ring of elm piles into the riverbed, filling the area inside with rubble, and then laying a floor of oak beams over the result. The Medieval London Bridge, ca. The bridge was possibly the strangest major bridge to be built in medieval times. It was completely asymmetrical. Of its twenty arches, no two were identical.
Nobody knows why.
It could be that Peter had to locate the bridges piers where the riverbed was firmest, and ended up shifting each pier a few feet this way or that to build on the firmest ground. Or perhaps he designed each arch based on how much building material he had at the time. Before the bridge was entirely completed in 1209, sections of it had already fallen down and been repaired, which suggests to me that the builders were learning how to build bridges as they went along. I hear you ask. However it was accomplished, the result was a bridge that would last for a long time.