Final answer:
Darius and Xerxes were related to (c) Persian kings. They were significant rulers of the Persian Empire, known for their administration, construction endeavors, and engagements in the Greco-Persian Wars.
Step-by-step explanation:
They were notable rulers of the Persian Empire during its peak, especially in its interactions and conflicts with the Greek city-states. Darius I and his son Xerxes I are famous for their ambitious construction projects such as the royal palace at Persepolis and for their military campaigns, including the Greco-Persian Wars in which they fought against the Greek city-states.
An example of their renowned works involved Darius I's systematic reorganization of the Persian Empire into various satrapies, or provinces, each overseen by a governor known as a satrap. This administrative reform was critical in managing such a vast empire, which spread across a significant portion of the ancient world. Moreover, the development of infrastructures like the Royal Road under Darius’s reign enhanced communication and governance across long distances within the empire.
Xerxes I, following his father's footsteps, also led vast expeditions, most notably the invasion of Greece during the Greco-Persian Wars. His military ventures, while initially successful, eventually faced major setbacks like the battles of Salamis and Plataea, ultimately limiting Persian expansion into Europe.