Possible Clues:

• The horse was wounded by the rough road
• Such rough going gave the horse a wound
• Like old streets
• Type of road made of small rounded stones
• One worked on foot on this sort of old street
• The road was so rough that it's only to a certain degree at last
• The surface was so rough that the horse was wounded
• The horse got injured by the rough road
• That was the bloody horse for a rough road
• Worked at last when swan was clearly wounded