By the middle of the 6th century BCE, the Achaemenids overthrew the Medes and incorporated Arachosia, Aria, and Bactria within its eastern boundaries. An inscription on the tombstone of Darius I of Persia mentions the Kabul Valley in a list of the 29 countries that he had conquered. The region of Arachosia, around Kandahar in modern-day southern Afghanistan, used to be primarily Zoroastrian and played a key role in the transfer of the Avesta to Persia and is thus considered by some to be the "second homeland of Zoroastrianism".