It's about 200 times as long as a Giant Tortoise's Lifespan.
In other words, 551 centuries is 220 times the length of a Giant Tortoise's Lifespan, and the length of a Giant Tortoise's Lifespan is 0.0045 times that amount.(for Adwaita, an Aldabra Giant Tortoise) (Dipsochelys dussumieri, formerly Geochelone gigantea)
It's about 600 times as long as Pepi II's reign.
In other words, the length of Pepi II's reign is 0.002 times 551 centuries.(a.k.a. Neferkare) (2278 BCE - 2184 BCE)
It's about 1,500 times as long as Pius IX's reign.
In other words, 551 centuries is 1,741 times the length of Pius IX's reign, and the length of Pius IX's reign is 0.0005744 times that amount.(a.k.a. Pope Blessed Pius IX, a.k.a. Giovanni Maria Mastai-Ferretti) (1792-1878)
The longest reigning Pope in the Church's history, Pius IX reigned from June 16th, 1846 to February 7th, 1878 — 0.3165 centuries. As the last monarchical Pope, he ruled over 3,000,000 subjects in the Papal States until 1870.
It's about 4,500 times as long as FDR's Presidential Term.
In other words, 551 centuries is 4,551 times the length of FDR's Presidential Term, and the length of FDR's Presidential Term is 0.0002197 times that amount.(a.k.a. Franklin Roosevelt, a.k.a. Franklin Delano Roosevelt) (1933-45)
It's about 6,000 times as long as King Tut's reign.
In other words, the length of King Tut's reign is 0.0002 times 551 centuries.(a.k.a. Tutankhamun, a.k.a. Tutankhaten, a.k.a. tVwa:t-ʕa:nəx-ʔaˡma:n) (1333 BCE - 1324 BCE)
Pharaoh of the 18th dynasty, Tutankhamun begin his reign at the age of eight in 1333 BCE and remained pharaoh until 1324 BCE — 0.09 centuries later. When artifacts from Tut's tomb were on display at the Metropolitan Museum of Art (New York City, New York) from late 1976 to 1979, they were viewed by an estimated 8 million people.
It's about 6,500 times as long as The Revolutionary War (American).
In other words, 551 centuries is 6,576 times the length of The Revolutionary War (American), and the length of The Revolutionary War (American) is 0.0001521 times that amount.(a.k.a. American War of Independence) (1775-83)
The War between Great Britain and the its thirteen colonies in North America (now the United States) for the independence of the United States is generally considered to have started with the Battle of Lexington and Concord on April 18th, 1775 (sometimes known as "The Shot Heard 'round the World") and to have concluded with the signing of the Treaty of Paris on September 3rd, 1783 — 0.08378 centuries. A total of 25,000 Americans are estimated to have died as a result of the war.
It's about 8,500 times as long as The Construction of the Chunnel.
In other words, 551 centuries is 8,625 times the length of The Construction of the Chunnel, and the length of The Construction of the Chunnel is 0.0001159 times that amount.(a.k.a. Channel Tunnel, a.k.a. Le tunnel sous la Manche) (1987 thru 1994) (Folkstone, Kent, UK to Coquelles, Pas-de-Calais, France)
The construction crew of the Chunnel broke ground in England on December 15th, 1987 and the tunnel was inaugurated by the Queen of England and the President of France on May 6th, 1994 — a total construction time of 0.06382 centuries. The 4.9 million cubic meters of chalk excavated from the UK side of the Chunnel was dumped within sea walls to create the 299,467.38 sq. km (74 acre) Samphire Hoe County Park near Dover, Kent.