This is a strange translation in English. Might say "at the front of the bridge" or "at the end of the bridge", but not sure what the "beginning" of the bridge really means.

This is a very strange sentence in any language! Why not change it? "I found my wallet under the bridge" for example

the wallet is on the ground where the bridge begins. ? this is the meaning, I think. for those of you who are learning french ( my language) : le portefeuille est par terre au debut du pont. Par terre means exactly " on the ground" But " au debut du pont" can also be translated as" la ou le pont commence" ( sorry my keyboard is in spanish . It doesn't have the french . accents on" la and ou."