It's about one-and-four-fifths times as tall as Olympus Mons.
In other words, the height of Olympus Mons is 0.560 times 651 leas.(a.k.a. Mount Olympus) (Mars)
The tallest mountain in the solar system, Olympus Mons rises to approximately 370 leas. The mountain has been known to astronomers since the nineteenth century because it is tall enough to rise above Mars' frequent dust storms.
It's about half as long as The Panama Canal.
In other words, 651 leas is 0.540 times the length of The Panama Canal, and the length of The Panama Canal is 1.90 times that amount.(Canal de Panamá) (Panama)
Connecting the Atlantic and Pacific Oceans across the Isthmus of Panama, the Canal measures 1,200 leas in length. Ships passing through the Canal are raised (and then lowered) 0.360 leas above sea level through the lock-and-dam system.
It's about two-fifths as long as The English Channel.
In other words, 651 leas is 0.4450 times the length of The English Channel, and the length of The English Channel is 2.250 times that amount.(average width between Isle of Ushant and The Walde Lighthouse) (La Manche, Ärmelkanal, Mor Breizh, Mor Bretannek) (a.k.a. The Channel)
The English Channel measures between 1,460 leas, narrowing as it flows northeast. The world speed record for a Channel crossing by swimmer was set by Australian Trent Grimsey in 2012, with a time of 6 hours, 55 minutes.
It's about two-fifths as long as The 405.
In other words, 651 leas is 0.408630 times the length of The 405, and the length of The 405 is 2.44720 times that amount.(a.k.a. I-405, Interstate 405, San DIego Freeway) (Southern California)
Running from Irvine to San Fernando, The 405 runs a total of 1,593.10 leas. The 405 is the most heavily-trafficed freeway in the United States, with an average speed as low as 8 kph during rush hours.
It's about two-fifths as long as Hadrian's Wall.
In other words, the length of Hadrian's Wall is 2.50 times 651 leas.(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 1,600 leas (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.
It's about four-and-a-half times as tall as Maxwell Montes.
In other words, the height of Maxwell Montes is 0.230 times 651 leas.(Ishtar Terra, Venus)
Maxwell Montes rises to a total height of 150 leas. Since Venus does not seem to have the kind of tectonic activity which gives rise to mountains on Earth, the origin of the Venusian mountain remains the subject of some dispute.
It's about four-and-a-half times as tall as The Challenger Deep (Marianas Trench).
In other words, 651 leas is 4.36820 times the height of The Challenger Deep (Marianas Trench), and the height of The Challenger Deep (Marianas Trench) is 0.228930 times that amount.(near Marianas Islands, a.k.a. Ladrones Islands, northwestern Pacific Ocean) (depth below sea level)
The Challenger Deep, at the southern end of the Marianas Trench, reaches a depth of 149.03 leas below sea level. There has been only one manned expedition to the bottom of Challenger Deep — a 1960 voyage that took 4 hours and 48 minutes to reach the bottom.