Complex sentence: Very few empires lived twice and even fewer lived with their former glory and power, one of them was Sassanid dynasty which indeed was the true heir of older Persian empire of Achaemenid dynasty.
Split into simpler sentences: Very few empires lived twice and even fewer lived with their former glory and power. One of them was the Sassanid dynasty which indeed was the true heir of the older Persian empire of the Achaemenid dynasty.