The city’s nearly-perfect street grid dotted by parks became a model for the rest of America.

This week Pennsylvania’s founder turns 375 years old. The ghost of William Penn may have celebrated the occasion from his stately resting place, which is all the way across the ocean in Buckinghamshire, England.

After nearly four centuries, Penn’s efforts still play a big role in modern life — and we’re not just talking about the way his City Hall statue looks like it has a boner when viewed from the Benjamin Franklin Parkway.

Among his greatest accomplishments is, of course, Philadelphia. What, you thought the greatest city in the world just happened? The Quaker leader planned our metropolis meticulously.

Philadelphia is widely known as the earliest attempt at “utopian city planning,” aka a city with a purposely crafted and curated center.

Penn dreamed that Philly, while urban, would still look like “a greene country towne, which will never be burnt and always wholesome.” (We’ve done ok living up to that goal — other than that time a guy ate horse poop off the street after the Eagles won the Super Bowl.)

Some of Penn’s proposals and creations have lasted to this day, and naturally, some did not. Here’s how Penn’s vision has manifested in Philadelphia.

The location

Like many great stories, Philadelphia’s origin starts with settling a debt.

In March of 1681, King Charles II couldn’t afford to pay back some money he owed to Penn’s dad. But he had something else to offer.

There was a bunch of land southwest of Jersey and north of Baltimore that Chuck wasn’t using. To make things even with Sir Penn the Senior, he gave the territory to Billy and told him to do whatever he pleased.

The 37-year-old Penn was suddenly the proud new owner of 45,000 square miles of land. First, he decided to set up an urban center at the spot where the Schuylkill and Delaware rivers met, figuring it would be easiest to establish a mecca for trade.

With the help of protege Thomas Holme, Penn mapped out a two-mile-wide rectangle of land bordered on both sides by fresh, flowing water. Say hello to Center City.

The perfect street grid

Philadelphia’s almost entirely regular street grid didn’t happen by accident. Aside from a few arterial roadways and rogue neighborhood pathways, the city’s central core boasts streets so aligned that they look like they went to military school.

Intersected by a few wide roadways, the countless side streets were designed to be the same width — “uniform down to the water.” The lots were spaced out perfectly on a map, with enough room to build a home in the middle and gardens on either side.

It’s so good that a century later, Washington, D.C. designed its grid the same way. For that, we can thank our pal Billy.

The public spaces

If you’re looking at Philly from above, you’ll notice there are four Center City parks — each one a mirror image reflected across the central streets of Broad and Market. That’s not an accident.

Penn thought up the idea of having “public squares” in his city. Each park would inject a neighborhood of Philadelphia with a dose of green space:

Logan Square (now Logan Circle)

Franklin Square

Washington Square

Rittenhouse Square

There’s also the center square, which after Penn’s death became home to City Hall.

All of this fed into his vision of a “greene country towne,” which was crucially important to Penn. His native London was devastated by fire and plague in the 1600s, and he brainstormed that more green space would prevent the quick spread of such catastrophes in his new home.

The core of Philadelphia in 2019 may not look all that green, but Penn’s four public parks endure — and even more public spaces have been added.

The wide streets

Perhaps in the modern day, Broad Street doesn’t look spectacular, since cities and towns all over the country have highways and five-lane roads. But in the 1600s, such wide streets were totally unheard of.

First among his urban planning colleagues, Penn’s blueprints included 100-foot-wide avenues, which at the time were broader than any street in London. Roads fronting the river were designed to be 60 feet wide, with the remaining streets were 50 feet wide.

Some experts say Penn was likely influenced by Richard Newcourt, a British cartographer who considered spacious roadways in his plans for rebuilding the parts of London that had burned down in the fire of 1666.

Still, Penn’s wide open streets were revolutionary. And to this day, they’re home to some breathtaking behavior.

The names of those streets

Ever notice a pattern to the names of Center City streets? If not, we’re about to blow your mind.

Going north to south, almost all of our avenues are named after types of trees. Though some have been renamed, they were designed with uniformity. There’s Vine, Sassafras (now Race), Mulberry (now Arch), High (now Market), Chestnut, Walnut, Locust, Spruce, Pine and Cedar (now South).

Disclaimer: In 2019, historians aren’t sure if the street names were specifically directed by William Penn himself. But since the dude designed the entire grid — and since he seems like a major control freak — he very well may have been involved in the naming process.

The modern development boom

Perhaps Penn’s greatest legacy is that he left so much wiggle room for the modern day. In mapping out Philly, the city architect intentionally left a whole bunch of space totally blank — with the goal of inspiring future development.

On the map created by his protege, Holme, Center City is almost dominated by lots that are unlabeled. Those blank spaces represent room for opportunity.

Penn also put forth plans to incentivize growth to the city’s outside neighborhoods.

He established a community then called the Liberty Lands, which was comprised of vacant farmland that would be given out to the first people to buy lots in Philly’s central core. That neighborhood is now known as Northern Liberties.

Over the centuries, Penn’s vision for the Philadelphia influenced many other American metro centers.

“This plan was the first city plan in the United States to provide for long-term urban growth,” reads a document from the American Society of Civil Engineers. “These features inspired the planners of many cities to adopt the Philadelphia Plan as a model.