Zarathustra was a Persian prophet that promoted his monotheistic religion, Zoroastrianism. The faith introduced the idea of heaven and hell to the people. The religious beliefs were later written down in the book, Avestas.

Under the leadership of Cyrus the Great, the Persians conquered most of the lands from the Aegean Sea to the borders of India.

The Achaemenid Empire, also known as the First Persian Empire, was the name of the empire of Cambyses. It united Mesopotamia, Egypt, and India; it was the most diverse empire at that time.

The Persian Wars were a series of battles between Greece and Persia. It was over territory and clashed when some Greek colonies rebelled against Persian occupants.

Succeeding Cyrus the Great, Cambyses conquered Egypt and parts of Southeast Europe. His empire became known as the Achaemenid Empire and it united three of the earliest centers of civilization-- Mesopotamia, Egypt, and India-- into one great empire.

Darius divided his lands into satraps with a satrap, who was a ruler of a province that were responsible to the emperor and not local leaders. He had inspectors that would report to the king of the satraps' behaviors. He also instituted a tax payment in order to fund great projects.

Xerxes, the successor of Darius, was very tolerant of diversity and even built a Gate of All Nations, which showed his honor to his subjects.

Persepolis was the capital city of Persia which is located in present day Iran. It was a very celebratory city and celebrated the artistic traditions of several groups.

Darius also instituted a common currency across the whole empire. This made trade more simple and efficient, and therefore promoted prosperity.

The Battle of Marathon was at the city of Marathon and was when an outnumbered Atheian army defeated the Persian forces of Persia, who then withdrew from Greece.

In the Battle of Salamis the Athenians defeated the Persians in a naval battle. Soon after the Athenians won other sea and land battles resulting in Persia's decline.

The Battle of Thermopylae was when Xerxes mustered a force of thousands and completely destroyed a few hundred Spartans and their allies. This battle led to the formation of the Delian League.

The Royal Road spanned 1500 miles and was the most famous of the network of roads built to encourage trade. Darius also added an efficient courier service with postal stations along the road.