At the narrowest part of the Bosphorus, Sultan Mehmet the Conqueror ordered the great fortress of Rumeli Hisarı to be built on the European shore in order to control commercial and military traffic in preparation for the siege of Constantinople.
He pitted his pashas (generals) against one another, daring them all to be the first to complete his particular tower and crenellated walls. The competition was fierce, and the huge fortress was completed in only four months.
Once completed, Rumeli Hisarı, along with Anadolu Hisarı on the Asian shore just opposite, controlled all traffic on the Bosphorus, and cut the city of Constantinople off from resupply by sea from the north.
The view of the 
The mighty fortress's useful military life was less than one year. Mehmet's armines conquered the Byzantinecapital several months later, and then there was no need for Rumeli Hisarı.
The fortress was used as a rather large and impressive Bosphorus toll booth for awhile, then as a barracks, later as a prison, and finally as an open-air theater, but never again as a fortress.
Within the fortress are a ruined minaret from the little mosque that served the garrison, and a more modern open-air theater where, in the 1960s, I saw a good production of Shakespeare's A Midsummer Night's Dream...in Turkish. (So far as I know the theater is seldom used for public theater these days.)
Located just north of the European Bosphorus town of Bebek, you can visit Rumeli Hisarı any day of the week except Wednesday, when it's closed, from 09:30 am to 16:30 (4:30 pm). There's a small admission fee of a few liras.
Note: don't bring a picnic or snack, as no food is allowed in the fortress (only water).
The theater and ruined minaret within.
Also, none of the rough stone staircases up to the walls, or the ramparts atop the walls, has a guardrail, so be very careful. A fall means serious injury or death.
Above the towns of Rumeli Hisarı and Bebek you'll notice the New England 19th-century-style architecture of Bogaziçi Üniversitesi (Bosphorus University), formerly Robert College, founded by the American Board for Foreign Missions over a century ago.
You can take Bus 25E (Kabataş—Sarıyer) to reach the fortress. Get out at the Rumeli Hisarı stop. You can also make Rumeli Hisarı a stop on your southward land excursion after a northward Bosphorus cruise.More...
Rumeli Hisarı
İstanbul Müzeler Hisarlar Müdürlüğü
Yahya Kemal Caddesi No. 42
Rumelihisarı, Sarıyer, Istanbul
Tel: +90 (212) 263 5305
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