I followed the road to Sparta.
This could mean two things, which will become clear if you add more context:
Departing Athens I took the road to Sparta. I followed the road to Sparta for twenty minutes, until I came across a soothsayer's booth.
This means there is a road to Sparta, and I followed it.
I departed Gytheion for Sparta and took the main road to Megalopolis. I knew that road passed by Pharis and Sparta, so I followed the road to Sparta and found lodgings in a sparsely furnished, uncomfortable inn (so I knew I had arrived in the right city).
This means there is a road to Megalopolis, and I followed it until I reached Sparta.
In the former example, the road to Sparta is best considered a unit: the phrase to Sparta can be said to belong to the road, and not to the verb followed directly.
In the latter example, to Sparta modifies the verb followed: it does not belong with the word road specifically.
In Greek, when you want to indicate that a certain phrase belongs to a specific noun, you can do this by repeating the article after the noun and before the phrase, as it was done in your text.