Using Bedouins as guides, Cambyses, the Persian king, conquered Egypt easily, after defeating King Psamtik III.

Despite his initial success, Cambyses (r. 525 - 522) faced subsequent crises. His entire army was lost in the deserts on his way to Siwa Oasis in the west. Historians are trying nowadays to find traces of this lost army.
Another expedition was sent to Napata but was also unsuccessful.
Cambyses left Egypt few years after the invasion, leaving satraps who governed the country. Greek historian Herodotus said Cambyses went insane because of his military failures in Egypt. He also described him as sacrilegious.
Hereinafter, Persian kings will adopt a remote reign of Egypt and depend on local satraps to control it.

Darius I hunting on his chariot in a trilingual cylinder-seal, engraved with his name image 2004 © www.clipart.com

After internal unrest in Persia, Darius I (r. 521 - 486) succeeded Cambyses. He was more interested in the country's internal affairs. His reign was a renewed prosperity for Egyptians.
He had the desire to reconcile with the people by respecting their religions. In this context he reconstructed the temple of Hibis at El-Kharga Oasis dedicated for God Amun and restored other temples. He continued digging the canal between the Red Sea and the Nile that Nekau II of the 26th dynasty initiated.

Challenges facing Darius mounted after the Greeks defeated the Persian army at the battle of Marathon.
Furthermore, Egyptians revolted and resisted the Persians but their revolt was later suppressed by Xerxes (r. 486 - 466), the next Persian king, who ruled for 20 years.

Xerxes I image 2004 © www.clipart.com

When Xerxes ascended the Persian throne he had to face the Greeks again. On the other hand, he appointed his brother, Achaemenes, as a satrap in Egypt whose cruelty caused Egyptians to revolt again. Achaemenes was finally assassinated.

Artaxerxes I (r. 465 - 424), then took power and in at attempt to quell Egypt fought two of its prominent princes; Inaros of Heliopolis and Amyrtaeus, who is probably the one who established the 28th dynasty at Sais.
Although Athenians aided Egyptians in their resistance Inaros was finally executed.

Darius II (r. 424 - 404) and Artaxerxes II succeeded respectively King Artaxerxes I. Once again revolts were associated to their rules. Inter-familiar conflicts of the Persians were giving Egyptians the opportunity to rise.