Understand
English name of the bay comes from its Greek counterpart, Hrison Keras ΧÏÏ ÏÏν ÎÎÏαÏ, which literally translates "Golden Horn". The "horn" part perhaps comes from the deep curve the bay has towards its end in the northwest. "Golden" part is more obscure, but possibly it's a poetic referral to reflections on the Horn's water during beautiful sunsets.
History
Golden Horn, an estuary formed by flooding of valleys of two rivers confluenting just northwest of Eyüp by Bosphorus in prehistorical times, had always been Istanbul's primary harbour. In fact, it can be argued that Istanbul would never have existed in such a grand way if it weren't for this superb harbour and also the superb trading route through and across Bosphorus, by the way.
In 1700s, mansions and large gardens full of tulips along the Horn, then called Sadabad, were favourite retreats of Ottoman state elite, who conducted costly parties thereabouts, which were later accused of economic destruction and the eventual dissolution of Ottoman Empire. Those years were called either Lale Devri "Tulip Era" or Sefahat Devri "Debauch Era" by different classes of society. Very little is left from that period physically. Then, about a century later, in 1800s, the banks of Golden Horn was where the industrial revolution first started in Ottoman Empire and up to 1980s, Golden Horn continued to be one of the industrial powerhouses of the Turkish economy, however this situation had its heavy toll on what was once "golden" Horn: the industrial effluents in addition to the untreated wastewater from rapidly expanding city's sewers caused the Horn stinking to high heaven, as much as that people were actually trying to avoid the avenues along its banks even if those routes meant a shortcut to where they are heading. Then in late 1980s, the first attempts to bring the Horn to its former glory began. Today its water is much cleaner although not clean enough for a swim and there is still some way to go, and pleasant parks on the lots of demolished factories surround its banks. Neighbourhoods on its banks, Eyüp in special, put a special emphasis on celebrating the Ottoman roots of the area.