The foundation of this majestic citadel was laid by the Emperor Akbar, and it developed as a stronghold of the Mughal Empire under successive generations. The curved bastions of the huge walls are interrupted by impressive gates, of which only the Amar Singh gate is now open to the public. The original and grandest entrance was through the Delhi Gate, which leads to the inner portal called the Hathi Pol or Elephant Gate. The graceful Diwan-i-Am or the Hall of Public Audiences, made of red sandstone, was constructed by Shahjahan in 1628. Within the Fort complex is the perfectly proportioned Moti Masjid, or Pearl Mosque, built by Shahjahan between 1646 and 1653. A Persian inscription within the mosque likens it to a perfect pearl. A marble tank stands at the centre of its spacious courtyard. The Agra Fort houses the Royal Pavilions, which were designed to catch the cool breeze wafting across the river. Other attractions comprise of the Macchi Bhawan, or the Fish Palace, the Hammam-i-Shahi, or the Royal Bath, the Nagina Masjid, or the Gem Mosque, made entirely of marble and the Zenana Meena Bazaar, where the ladies of the court would browse through goods like silk, jewellery and brocade. Past the Chittor gate, installed in 1568, is the Diwan-i-Khas, or the Hall of Private Audience, built by Shahjahan in 1636 - 37. Here, the emperor would receive kings, important dignitaries and ambassadors. The famous Peacock Throne is said to have been kept here, before being shifted to Delhi by Aurangzeb. Tucked away by the west wall of the hall is the Mina Masjid or the Heavenly mosque, where Shahjahan prayed when he was imprisoned in the Fort by his son Aurangzeb. A doorway from the rear of the Diwan-i-Khas leads to the Mussaman Burj, or Octagonal Tower, a two-storeyed pavilion, where Shahjahan caught his last glimpse of the Taj Mahal before he died. Built for his beloved Mumtaz Mahal, this is another example of Shahjahan's immense creativity. The Khas Mahal, or the Private Palace, was used by the emperor as a sleeping chamber, and is designed for comfort, with cavities in the room to insulate against the heat. The Mahal is flanked by two golden pavilions. Other ornate palaces within the Fort are the Sheesh Mahal (Palace of Mirrors), the Shah Jahani Mahal (Shahjahan's Palace), Jehangir Mahal (Jehangir's Palace) and the Akbari Mahal (Akbar's Mahal).