Madrid is the capital of the country, the 3rd largest city in the EU. In the mid 9th century, Muhammad I of Cordoba constructed a small castle where the Royal Palace now stands. The Moors built a citadel, al-Mudayna, around this castle. They named the area after the nearby Manzanares River, which the muslims called al-Majrit. From this came the name Majerit, later spelled Madrid.