Achaemenid Empire
The Achaemenid Empire was the largest empire during ancient times. The Achaemenid Empire lasted from 550 B.C.E. to 330 B.C.E.. Cyrus the Great was the founder of the Achaemenid Empire. Although Cyrus the Great was a renowned ruler of the Achaemenid, his successors were not as good as a ruler as Cyrus was. Cyrus's son, Cambyses II, was killed during a revolution led by Gaumata, who posed as Cambyses's brother, Bardiya. Gautama was later deposed by one of the descendants of Cambyses, named Darius the Great. He attacked the Greeks, and as a result, shortened the Achaemenid Empire's territorial reach. The Achaemenids were later conquered by Alexander the Great, also known as Alexander of Macedonia, in 330 C.E..
http://www.iranchamber.com/history/achaemenids/achaemenids.php
http://www.iranchamber.com/history/achaemenids/achaemenids.php
Parthian Empire
Succeeding the fall of the Achaemenids, a new empire rose in Persia. It was the Parthian Empire, which began in 247 B.C.E. and ended in 224 C.E.. The Parthian Empire was ruled by Seleucus I, who was Alexander the Great's successor after he died in 323 B.C.E.. It was during this empire's existence in which the Hellenistic culture had massively spread. The Seleucids had a rivalry with the Egyptian Ptolemies, the Parni invaded the Parthian Empire and overthrew the Seleucus dynasty. A new ruler emerged in 237 B.C.E., named Arsaces. The Parthians attempted to invade the Romans, but had disastrous results. Subsequently, the Parthians created a peace treaty with Augustus, the king of the Romans at that time. The Parthian empire lasted for 500 years, but was ended when the Sassanids from the southwest attacked and destroyed the Parthian Empire.
http://www.metmuseum.org/toah/hd/part/hd_part.htm
http://www.metmuseum.org/toah/hd/part/hd_part.htm
Sassanid Empire
The Sassanid Empire lasted from 224 C.E. to 651 C.E., and its land's size was very similar to, but still smaller than the Achaemenid Empire's land. The Sassanids established a capital at Ctesiphon, around 25 miles south of current-day Baghdad, Iraq. In 224 C.E., Ardashir I attacked and ended the Parthian Empire, and subsequently created the Sassanid Empire. During the Sassanid Empire's existence, the usage of coins was increased. In addition, it's main religion was Zoroastrianism. It's invasions allowed for the empire to expand in size, and eventually, the empire extended from the Euphrates River to the Indus River. During the 5th century, the Sassanid empire was attacked by the Hephthalite Huns. The Huns weakened the empire's power, and resulted in revolts within it. The empire was ended when the last Sassanid emperor, Yazdegerd III, died in 651 C.E..
http://www.metmuseum.org/toah/hd/sass/hd_sass.htm
http://www.metmuseum.org/toah/hd/sass/hd_sass.htm