Why it's the capital
After Ottoman forces destroyed the old Saudi capital, Diriyah, in 1818, Turki ibn Abdallah made Riyadh the new capital in the 1820s. In 1932 Ibn Saud named his kingdom Saudi Arabia, with Riyadh as its capital.
Capital of Saudi ArabiaIn the middle of Saudi Arabia, Riyadh spreads across the eastern part of the Najd plateau, on the east bank of Wadi Hanifa, at about 600 m above sea level.
After Ottoman forces destroyed the old Saudi capital, Diriyah, in 1818, Turki ibn Abdallah made Riyadh the new capital in the 1820s. In 1932 Ibn Saud named his kingdom Saudi Arabia, with Riyadh as its capital.
Aim near the middle of Saudi Arabia, a little east of centre: Riyadh is deep inland, much closer to the Persian Gulf coast than to the Red Sea.
Sources: Wikipedia: Riyadh, Wikipedia: Najd