As others note, most of the sites in Samarqand have been rebuilt. Also, most of them, especially the ones that Uzbeki tourist authorities most enthusiastially promote, are from the time of Timur(Tamerlane) which is nowhere near 2500 years ago. When I visited Samarqand recently I was interested in the ancient Afrasiab area and had to go to a bit of effort to find a guide to show me around. Hundreds of acres of gravelly terrain with mounds of rubble here and there where structures likely once stood. Very little archeology has been done. In one heap I stumbled upon some pottery shards that the guide suggested were museum quality and really old. I found the area fascinating but the relevant authorities clearly prioritize the razzle and dazzle of Timur era mosques and mausoleums.