The Kizilirmak (Kizil Irmak) River was known as the Halys River in ancient times. The river flows past the Turkish town of Bafra into the Black Sea. Notice the Halys between Sinope and Amisos on the map below. It is about 35 to 40 miles west of Amisos. The river to the east of Amisos is the Iris.
Pfeiffer and Vos describe the importance of the Halys.
The most important river of the peninsula [Asia Minor] is the Kizil Irmak (ancient Halys), 600 miles long, which originates in eastern Asia Minor and flows in a great bend to the southwest and finally into the Black Sea through what was Pontus. Unfortunately its gorge is often too narrow to permit it to be an important means of communication into the interior. (The Wycliffe Historical Geography of Bible Lands, 316).
The photos below show the river flowing from the mountains on the south side of Pontus. These photos were made about 10 miles from the Black Sea, which is to the north. This is one of the widest areas of what was once the Roman province of Pontus.
C. J. Hemer wrote of the importance of the rivers of Pontus. He also calls attention to the fact that the “narrow coastal margin was separated from the interior by mountains.”
The chief rivers besides the Halys were the Iris, Lycus, and Thermodon. The fertile land of their valleys and of the narrow coastal margin was separated from the interior by mountains, once heavily forested, which have always impeded communication with the plateau. Important products included fruit, corn, olives, and timber. (The International Standard Bible Encyclopedia, Revised (3:903).
The ancient Hittite Empire comes to mind when I think of the Halys River, as Pfeiffer and Vos have pointed out. We say that the Hittites lived within the bend of the Halys River. A portion of Cappadocia (1 Peter 1:1) is also within that same bend.
Seeing the Halys, which I had seen before near the Hittite capital, was a pleasant surprise.