From the mouth of the Lycus to that of the harbour, this arm of the Bosphorus is more than seven miles in length.

The entrance is about five hundred yards broad, and a strong chain could be occasionally drawn across it, to guard the port and the city from the attack of an hostile navy.
"Between the Bosphorus and the Hellespont, the shores of Europe and Asia receding on either side include the Sea of Marmora, which was known to the ancients by the denomination of the Propontis.

The navigation from the issue of the Bosphorus to the entrance of the Hellespont is about one hundred and twenty miles.

Those who steer their westward course through the middle of the Propontis may at once descry the highlands of Thrace and Bithynia and never lose sight of the lofty summit of Mount Olympus, covered with eternal snows.

They leave on the left a deep gulf, at the bottom of which Nicomedia was seated, the imperial residence of Diocletian, and they pass the small islands of Cyzicus and Proconnesus before they cast anchor at Gallipoli, where the sea which separates Asia from Europe is again contracted to a narrow channel.
"The geographers, who with the most skilful accuracy have surveyed the form and extent of the Hellespont, assign about sixty miles for the winding course and about three miles for the ordinary breadth of those celebrated straits.