Persia is the now obsolete name of Iran, today used only to refer to the ancient Persian empire. The name was given to it by the Greeks, and derives from the southern Fars province of Iran where the Parsae lived. It was passed on to Persepolis, an ancient city built by the Persians and destroyed by Alexander the Great, and is also used about the Parsi community in India, Zoroastrians who were expelled from Iran by the Muslims.
The name of Persia was officially given up by the government in 1935, then allowed back into use in 1949. It is still associated with Oriental mystique, ornamented carpets, and a classic computer game. Yet its best claim to fame comes from the great Persian Empire.
Cyrus the Great united the Persians and the Medes to create the Achaemenian dynasty. Through his conquests, he created the greatest empire in the ancient world, reaching out to meet both the Arabian Sea, the Mediterranean, the Caspian Sea and the Black Sea.
Alexander the Great was the man who made the kingdom collapse. He conquered province after province, seemingly dreaming of a Greek-Persian empire which would be even greater than the one he was destroying. Unfortunately for him, he died before one could be created.
Persia now became the place to invade. The Hellenistic period was followed by the Parthian, then Arabs, Mongols and Turks descended upon it and took turns ruling it. Persia became a hot, hot melting pot of culture and language.
The Achemenids spoke Old Persian, a language brought by the Medians which closely resembled Sanskrit. This developed further into Avestan and Pahlavi, the former a language used in the Zoroastrian Zend-Avesta, the latter the ancestor of modern Farsi. From the beginning, the Persians adopted several writing systems from abroad. They used Babylonian cuneiform for their monuments and Aramaic letters for documents. Today, Farsi is written with Arabic letters.
Confused yet?
To ease the troubled mind, I offer a chronological list of the many dynasties of Persia.
The Medians first established an Empire
The Achaemenid Empire, founded by Cyrus II, the Great
The Seleucid Empire was founded by Seleucid I after Alexander came, saw, conquested, and died.
The Parthian Empire was made by Mithridates I
The Sassanid Empire grew under Ardeshir, a descendant of Sassan
Muslim invaders established the caliphate ruled by the Abbasid Dynasty, later to be overrun by local Buyawids
The Seljuks, led by Toghrul Beg, then took over
The Mongol Hordes spread throughout Asia, and in Persia Tamerlane founded the Timurid Dynasty
The Safavid Empire was founded by Shah Ismail
The Qajar Dynasty was founded by Agha Muhammed Khan and ruled what is now Iran until the revolution.
Cities (which belonged to the Persian Empire at some stage)
Babylon -
Baghdad -
Damascus -
Herat -
Isfahan -
Jerusalem -
Kerman -
Khorassan -
Meshed -
Pasargadae -
Shiraz -
Susa -
Tabriz -
Tehran
Of interest, I'm sure, is also Persian Mythology as well as the Persian Wild Ass. | 
