According to Wikipedia:

"Around 518 BC, construction of a broad stairway was begun. The stairway was planned to be the main entrance to the terrace 20 meters above the ground.

"The dual stairway, known as the Persepolitan stairway, was built in symmetrically on the western side of the Great Wall."

"The 111 steps were 6.9 meters wide with treads of 31 centimetres and rises of 10 centimetres. Originally, the steps were believed to have been constructed to allow for nobles and royalty to ascend by horseback."

"New theories suggest that the shallow risers allowed visiting dignitaries to maintain a regal appearance while ascending. The top of the stairways led to a small yard in the north-eastern side of the terrace, opposite the Gate of Nations."

en.wikipedia.org/wiki/Persepolis

All I can add to that is to point out the wooden steps that have been built over the stone steps. I assume this is intended to protect the stine stairs from erosion caused by countless visitors' footsteps.

If one is eager to see what it feels like to walk directly on the ancient steps, there is an exposed area running the length of the stairs that will do just fine.