It marked the passing of the horse-drawn vehicle (3)
I believe the answer is:
rut
This could be a double definition.
'it marked' is the first definition.
The definition suggests a singular noun which matches the answer.
'passing of the horse-drawn vehicle' is the second definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'the' is the link.
Can you help me to learn more?
(Other definitions for rut that I've seen before include "hazard in the road" , "A worn groove - don't live in one" , "Well-worn track" , "Groove or furrow - don't get into one" , "Furrow or groove as in track" .)