Ghumdan Palace, also Qasir Ghumdan or Ghamdan Palace, is an ancient palace and fortress in Sana'a, Yemen. It is the earliest known castle in the world. All that remains of the ancient site (Ar. khadd) of Ghumdan is a field of tangled ruins opposite the first and second of the eastern doors of the Jami‘ Mosque (Great Mosque of Sana'a). This part of Sana'a forms an eminence which is known to contain the debris of ancient times. The place is located on the extreme southeastern end of Sana'a's old walled city, al-Qaṣr, just west of where the Great Mosque of Sana'a was later built, and is part of the UNESCO World Heritage Site of the Old City of Sana'a. It is sometimes referred to as Ghumdan Tower.
According to Arab geographer and historian, Al-Hamdani (c. 893-945), the foundation stones of Ghumdan Palace were laid by Shem, the son of Noah, and finished by the Sabaean monarch Ilī-Sharḥa Yaḥḍib (ca. 8th century BCE), the father of Bilqis. Others say that it was built by Sha'r Awtar who walled the city of Sana'a, while yet others suggest that it may date to pre-Islamic times, constructed by the Sabaeans during the reign of the last great Sabaean King El Sharih Yahdhib (ca. 60-20 BCE). Some historians date it to the beginning of the 2nd century or the 1st century. The palace was destroyed by Caliph Uthman, or even earlier, by the Abyssinian conqueror Abrahah Al-Hubashi. Restored several times, the palace history is represented in numerous legends and tales. It is mentioned in many pieces of Arabic poetry, the poets singing about its beauty. Ghumdan Palace tower, a 20-storey high-rise building, is believed by some to have been the world's earliest skyscraper.