The Old Forest Road, also known as Men-i-Naugrim ('Dwarf-Road') in Sindarin, was the name of the east road where it passed through the Anduin at the Old Ford and then through Mirkwood. The Enchanted river intersected it at a marshy point near the River Running.
It was about three-hundred miles in length.
It was probably laid out before or during the First Age to connect the dwarves of the Far East with their kin in the Misty Mountains, and from then on to those in the Blue Mountains. When they eventually met the elves, they made alliance with them and trade pacts were forged and the road was no doubt used to facilitate trade between them.
It is possible that during the late Second Age it was used to carry the armies of the Last Alliance, which may add to the evidence that it once had a bridge running across it that eventually rotted away, thus crossers had to rely on a boat to reach the other side of the road.
After Sauron's occupation of Dol Guldur, the forest of Mirkwood became more and more dark and dangerous, so most chose not to travel upon it for fear of being attacked. Most that did travel on it lost sight of it and usually never found their way back onto it again, thus never finding their way out of the forest according to Gandalf and Beorn.