I have read 'Conan' by Aubie56 and its not that one - I'm pretty sure it was on storiesonlie a while ago but was too be published by the author. Premise of the story from what I can remember is that they guy gets sent back in time to rome as a slave and then gets moved to a farm along a river and starts building ships after fixing the banks of the river - it was a pretty long story and I would love to read it again