I think I found what you are looking for:

According to the wiki:

"At the start of his journey to Volantis Tyrion Lannister takes the opportunity to have a closer look at the Valyrian road that he and Illyrio are traveling on. It runs as straight as a spear to the horizon. It is a ribbon of fused stone raised half a foot above the ground to allow rainfall and snowmelt to run off its shoulders. Tyrion muses that unlike the muddy tracks that pass for roads in the Seven Kingdoms, the Valyrian roads are wide enough for three wagons to pass abreast, and neither time nor traffic mar them. They still endure, unchanging, four centuries after Valyria itself had met its Doom."

The roads are made from fused stone that is built in a way that allows rain and snow to quickly run off the sides.

We can reason that this is a huge factor in it's preservation of it's condition.

As for if there is magic involved, the wiki isn't clear, but according to another page of the wiki Valyrian steel is magical. So there is a possibility some magic was used to create the roads.

I think I found what you are looking for:

According to the wiki:

"At the start of his journey to Volantis Tyrion Lannister takes the opportunity to have a closer look at the Valyrian road that he and Illyrio are traveling on. It runs as straight as a spear to the horizon. It is a ribbon of fused stone raised half a foot above the ground to allow rainfall and snowmelt to run off its shoulders. Tyrion muses that unlike the muddy tracks that pass for roads in the Seven Kingdoms, the Valyrian roads are wide enough for three wagons to pass abreast, and neither time nor traffic mar them. They still endure, unchanging, four centuries after Valyria itself had met its Doom."

The roads are made from fused stone that is built in a way that allows rain and snow to quickly run off the sides.

We can reason that this is a huge factor in its preservation and its condition.

As for if there is magic involved, the wiki isn't clear, but according to another page of the wiki Valyrian steel is magical. So there is a possibility some magic was used to create the roads.

I think I found what you are looking for:

According to the wiki:

"At the start of his journey to Volantis Tyrion Lannister takes the opportunity to have a closer look at the Valyrian road that he and Illyrio are traveling on. It runs as straight as a spear to the horizon. It is a ribbon of fused stone raised half a foot above the ground to allow rainfall and snowmelt to run off its shoulders. Tyrion muses that unlike the muddy tracks that pass for roads in the Seven Kingdoms, the Valyrian roads are wide enough for three wagons to pass abreast, and neither time nor traffic mar them. They still endure, unchanging, four centuries after Valyria itself had met its Doom."

The roads are made from a fused stone that is built in a way that allows rain and snow to quickly run off the sides.

We can reason that this is a huge factor in it's preservation of it's condition.

As for if there is magic involved, the wiki isn't clear, but according to another page of the wiki Valyrian steel is magical. So there is a possibly some magic was used to create the roads.

I think I found what you are looking for:

According to the wiki:

"At the start of his journey to Volantis Tyrion Lannister takes the opportunity to have a closer look at the Valyrian road that he and Illyrio are traveling on. It runs as straight as a spear to the horizon. It is a ribbon of fused stone raised half a foot above the ground to allow rainfall and snowmelt to run off its shoulders. Tyrion muses that unlike the muddy tracks that pass for roads in the Seven Kingdoms, the Valyrian roads are wide enough for three wagons to pass abreast, and neither time nor traffic mar them. They still endure, unchanging, four centuries after Valyria itself had met its Doom."

The roads are made from fused stone that is built in a way that allows rain and snow to quickly run off the sides.

We can reason that this is a huge factor in it's preservation of it's condition.

As for if there is magic involved, the wiki isn't clear, but according to another page of the wiki Valyrian steel is magical. So there is a possibility some magic was used to create the roads.