William Penn had more in mind for Philadelphia than just a collection of streets and houses when he first laid out his plans in 1682. He imagined a city where people of different faiths and backgrounds could live together in peace, based on tolerance, fairness, and civic harmony.

This was his “holy experiment.” Penn’s promise was very different from what people were used to. At a time when religious wars were tearing Europe apart, he offered a charter for Pennsylvania that guaranteed freedom of worship. People from many different religions—including Quakers, Lutherans, Catholics, Jews, and others—found safety in Philadelphia. The city became a place where diversity was valued long before the word became popular. This spirit of acceptance became part of Philadelphia’s DNA, making it a center for free press, a forum for revolutionary ideas, and a home for abolitionist thought.

The Declaration of Independence and the Constitution were debated and signed here because Philadelphia was a place where different ideas could coexist. Penn’s grid of streets, which had wide avenues with green squares on either side, was more than just a way to plan a city. It was a metaphor for being open, a city built to keep people from getting stuck in the narrow streets and hidden corners of Old World towns.

His plan showed that he thought that civic life should be open, easy to get to, and shared. The promise wasn’t perfect, of course. Native Americans were forced to leave their homes, and not all Philadelphians had the same rights. Still, the hope that a city could be built on brotherly love is one of Philadelphia’s most lasting gifts.

We are living in Penn’s experiment today when we walk by Independence Hall or through neighborhoods that were built by waves of immigrants. The city’s ability to adapt to new people and customs is proof of that founding vision. Philadelphia remembered is more than just a city of monuments. It is a city of promises, some of which have been kept and some of which have been broken, but they all ring out through the streets. Penn’s promise still challenges us: to see brotherly love not as a motto, but as a daily practice.