It's about one-and-a-half times as long as The Grand Canyon
In other words, 661 kilometers is 1.48 times the length of The Grand Canyon, and the length of The Grand Canyon is 0.676 times that amount.(a.k.a. Gran Cañón) (Arizona) (Colorado River miles measure)
The Grand Canyon has a total length of 446 km along the course of the Colorado River at its bottom. Having opened in early 2007, the Grand Canyon Skywalk allows tourists to stand on a horseshoe-shaped glass walkway 1.10 kilometers above the floor of Granite Gorge.
It's about half as long as The Rhine
In other words, 661 kilometers is 0.501 times the length of The Rhine, and the length of The Rhine is 2 times that amount.(a.k.a. Rhein, a.k.a. Rijn, a.k.a. Rhin, a.k.a. Rain, a.k.a. Reno, a.k.a. Rhenus, a.k.a. Ryn) (from near Reichenau, Switzerland through Hoek van Holland, Rotterdam, Netherlands)
The Rhine river runs 1,320 km in total length. The World War II Battle of Arnhem, as memorialized in the 1974 book and 1977 movie A Bridge Too Far, was the first of several attempts to capture key bridges across the Rhine, beginning with the Arnhem Bridge in the Netherlands.
It's about three-tenths as long as The Colorado River
In other words, 661 kilometers is 0.284 times the length of The Colorado River, and the length of The Colorado River is 3.52 times that amount.(a.k.a. Aha Kwahwat, a.k.a. Grand River, a.k.a. Tizon River, a.k.a. Tecon River, a.k.a. Tison River) (from Grand Lake, Colorado through the Gulf of California)
The Colorado River runs 2,330 km in length. Along this length, the river descends from its source, approximately 2.750 kilometers above sea level in the Rocky Mountains, to its mouth in the Gulf of California.
It's about one-fourth as long as The Danube
In other words, 661 kilometers is 0.232 times the length of The Danube, and the length of The Danube is 4.31 times that amount.(a.k.a. Donau, a.k.a. Dunaj, a.k.a. Dunav, a.k.a. Duna, a.k.a. Дунав (Dunav), a.k.a. Dunărea, a.k.a. Дунáй (Dunay), a.k.a. Tuna) (from Breg Martinskapelle, Black Forest, Germany through the Danube Delta, Romania)
The Danube river runs 2,850 km in total length. Intersecting Vienna, Austria; Bratislava, Slovakia; Budapest, Hungary; and Belgrade, Serbia, the Danube touches more capital cities than any other river.
It's about one-fifth as long as The Oregon Trail
In other words, 661 kilometers is 0.189 times the length of The Oregon Trail, and the length of The Oregon Trail is 5.29 times that amount.(from Independence, Missouri to Oregon City, Oregon)
The historic Oregon Trail stretched 3,490 km across five (sometimes six) states in the western United States. In the early years of the Trail's existence, the trip was estimated to have taken an average of 160 days.
It's about one-fifth as long as The Volga
In other words, 661 kilometers is 0.187 times the length of The Volga, and the length of The Volga is 5.35 times that amount.(a.k.a. Волга, a.k.a. İdel (Идел), a.k.a. Атăл (Atăl), a.k.a. Edil, a.k.a. İdil, a.k.a. Рав (Rav)) (from the Valdai Hills, Tver Oblast, Russia through the Caspian Sea)
The largest river in Europe, the Volga river runs 3,530 km in total length. World War II's Battle of Stalingrad between the Nazi Germany and the Soviet Union, which resulted in nearly two million casualties, was fought in part for control of the river.
It's about five-and-a-half times as long as Hadrian's Wall
In other words, 661 kilometers is 5.5 times the length of Hadrian's Wall, and the length of Hadrian's Wall is 0.18 times that amount.(a.k.a. Roman Wall, a.k.a. The Wall, a.k.a. Vallo di Adriano, a.k.a. Vallum Aelium, a.k.a. Severus' Wall) (from North Tyneside, Tyne and Wear, England, United Kingdom to Cumbria, North West England, United Kingdom)
Hadrian's Wall, which crossed England form the North Sea to the Irish Sea during the time of Roman rule, measures 120 km (about 79 Roman miles). Roman soldiers — at one time up to 10,000 of them — only occupied Great Britain for about 246 years after the wall was built, after which time the local Brits began to take residence the wall's garrisons.