Who Defended the Bridge?

The other evening our neighborhood friend who owns the Antietam Ironworks Inn asked me to use my fine Googling skills to find out which general defended the Antietam Ironworks bridge during the battle.  (He wasn't sure that in fact someone did, but he was under the impression that someone had.)
Unfortunately, I did not come up with a name or even that the bridge played any role in the battle except that Rebel troops crossed it in their journey to support Lee at Sharpsburg.  However, my short search did find that companies from the 13th Massachusetts camped here for a bit in 1861 (a year before the battle).  The letters at this site are very interesting glimpses into the soldiers' lives. I especially enjoyed a letter from James B. Noyes; apparently, the most memorable part of being in Antietam Village was the vicious attack of fleas!

Modern day defenders watching over the bridge