theromansmadesomegoodbridgesofstonesandmanyofthesearestillstandingtoday,sometimes,since,noonecouldbuildabridgeacrossariver中since是什么意思?

Question

the romans made some good bridges of stones and many of these are still standing today,sometimes,
since,no one could build a bridge across a river中since是什么意思?

Answer 1

至今,从那时以来