Beyazit Meydani, once the Roman Forum Tauri, now holds one of the city's largest Sunday flea markets.
Beyazit Square (officially named Hürriyet Meydani,"Freedom Square," but no one uses that name except some cartographers) is the spacious plaza in front of Istanbul University's main gate, and next to the Grand Bazaar and the Old Book Bazaar (Sahaflar Çarsisi).
Though the Romans called it the Forum Tauri, the Byzantines expanded it and renamed it the Forum of Theodosius.
The Mosque of Sultan Suleyman the Magnificent (Süleymaniye Camii), Istanbul's largest, is just behind the university enclosure.
The area just east of the square is known as Çarsikapi (CHAHR-shuh-kah-puh, "Door to the Market") because of a main entrance to the Grand Bazaar. At Çarsikapi you can catch the Eminönü/Kabatas tram eastward for Sultanahmet, Sirkeci Station and Eminönü (Egyptian Market, Galata Bridge).
A great way to explore Istanbul's markets is to take a walking tour from Beyazit and the Grand Bazaar north along Uzunçarsi Caddesi ("Longmarket Street") through the Tahtakale market district to the Rüstem Pasha Mosque and the Egyptian (Spice) Bazaar on the Golden Horn.
Going west, you catch the Zeytinburnu tram at either the Çarsikapi or Universite stops for Aksaray, Millet Caddesi, Topkapi gate and Zeytinburnu, where you can transfer to the Metro.