Flooding in Ellicott City, Md. caused road closures and home damage, including on Frederick Road. (Astrid Riecken/For The Washington Post)

In 1772, three Quaker brothers from Pennsylvania — Joseph, Andrew and John Ellicott — established a flour mill on the banks of the Patapsco River.

Ellicott City — or Ellicott’s Mills, as it was then known — was born.

The Patapsco River that powered the flour mill propelled the town to become one of the largest milling and manufacturing towns on the East Coast.

But over the years, the river has also unleashed its power on the town, wreaking havoc as raging waters overflow the riverbank, causing devastating flash floods to sweep through the streets.

The earliest and most destructive flood recorded came in 1868, when the Patapsco River rose five feet in 10 minutes.

In fact, as Harper’s Weekly reported at the time, the river at Ellicott City “rose ten feet before a drop of rain had fallen there, and was at one time forty feet high!”

That may be a bit of an exaggeration, but what is certain is that the Patapsco rose more than 20 feet and killed 43 people, according to the Baltimore Sun.

The flood of 1868 would go in history as the Great Flood.

More floods came in 1901, 1917, 1923, 1942 and 1952.

But it is the remnants of Hurricane Agnes, and the flood it caused in 1972, that people remember most in Ellicott City.

Agnes was one of the worst natural disasters Maryland has ever suffered. It pelted already soaked areas of the state with 10 to 14 inches of rain, killed seven people along the Patapsco River, forced 900 Howard County residents to evacuate their homes, left 700 temporarily homeless, and damaged close to 200 homes and dozens of businesses, according to the Sun.

In 2011, Tropical Storm Lee heaped another deluge onto Ellicott City. The historic city’s drains and channels buckled under relentless droves of rain — about five inches in just over two hours, and about 10 inches in total — and a flash flood was unleashed on the town’s streets, wreaking havoc in homes and businesses.

But if Agnes was a “once-in-a-lifetime” storm, as David Hoff, then a sergeant in the county fire department, described it to the Sun, then this past Saturday’s was even more momentous.

According to the National Weather Service, the Patapsco River rose 14 feet in about 90 minutes Saturday evening.

For so much rain to fall so intensely in any given year works out to be a 0.1 of a percent chance, the National Weather Service said.

Saturday’s storm, then, was a once-in-a-millennium occurrence.