Welcome to Secret Philly, an occasional series in which Billy Penn will visit hidden or exclusive places in Philadelphia and write about them.

Philly’s a city of old buildings, but you’d be hard-pressed to find one as impressive as the Armory of the First Cavlary Troop. Located in Center City, this booming fortress features turrets, a sally port, and a plethora of military history.

The Armory occupies an entire city block, bordered by 23rd, 24th Amory and Ranstead streets. Inside the Armory is a vast open drill hall, which you can rent for all kinds of events — from weddings to roller derbies.

But when the event lighting comes down and the vendors leave, there’s much more to see. Tanks and military vehicles park within, National Guardsmen come monthly to train, and a nearly 250 years of history are preserved behind its walls.

Inside the First Troop Armory's main hall as an event sets up. Jared Whalen/Billy Penn

So…what’s the castle for?

Built in 1901, the giant granite building houses the First Troop Philadelphia City Cavalry. Besides having a kickass building to call home, the First Troop has an impressive story behind it.

First Troop formed in 1774 and is the oldest continuously serving cavalry in the nation. Its history starts a few months after the First Continental Congress met in the same year, at which citizens of Philly put together a committee to determine the best way to resist the British and carry out the nonimportation resolutions of the Congress. On Nov. 17, three of the committee’s members, along with 25 other distinguished Philadelphia gentlemen, associated as the Light Horse of the City of Philadelphia, which later became the First Troop Philadelphia City Cavalry.

Unlike most modern military units, the Troop still operates on certain rights and privileges courtesy of two pieces of legislation, the Militia Act of 1792 and the Militia Act of 1903. It is one of, if the not the only, unit that can take advantage of the provisions of those acts because of its age. Which means the Troop is able to keep its founding privileges intact, like its democratic method of voting members into the unit and electing members into leadership positions.

Members of the First Troop are authorized to wear traditional uniforms that resemble those worn closer to the time of its formation. Jared Whalen/Billy Penn

Even with the traditions, the First Troop is still a functioning military unit of the Pennsylvania Army National Guard, seeing recent deployments to Kuwait, Iraq and Egypt. Membership has always been voluntary, requiring members in an active role to donate their drill pay back to the unit to follow the tradition.

To preserve the history of the cavalry unit, members learn to ride horseback and even handle a sword while mounted at the Troop’s horse farm in West Chester. Also of note, members of the unit are authorized to wear traditional dress uniforms dating back to its early days, as opposed to the modern Army Service Uniform.

Traditions, got it. But what’s in the castle?

Pass through the sally port (castle-speak for “big ass doorway”), and walk into the giant, open hall. The room is one of the largest enclosed spaces in the city and relies on ginormous trusses rather than on support beams. The absence of the beams allowed for horses and riders to practice maneuvers without any interference. Today, the hall houses the unit’s vehicles and has separate rooms for its training equipment and supplies.

The rooms outside the hall serve as both activity space and museum-like display areas.

The Noncommissioned Officers' Lounge with wet bar and leather couches. Jared Whalen/Billy Penn

First, there’s the quarters for the commissioned and noncommissioned officers. Mimicking motherland England in many ways, the Army kept the officers’ and the sergeants’ lounge areas separate. Each features a full bar.

On the walls of the quarters, as well as throughout the entire building, are paintings of the troops and portraits of the members. Of note, there are several paintings by the Rhode Island artist Gilbert Stuart, who is considered to be one of America’s foremost portraitists.

The mess hall features guideons from the unit's origins up to the present. Jared Whalen/Billy Penn

Move upstairs and step into the mess hall, a massive room that serves as both a dining area and ceremonial meeting room. In addition to paintings, the walls bear the various “guideons,” or flags, of the unit over time.

“During the time of the revolution, flags were not woven as patriotic symbols out on front door steps, Ryan Noyes, a member of the Troop, said. “They had an extremely functional and important meaning. They were essentially identifiers of the unit.”

While modernized with air conditioning and audio/visual equipment, the mess hall looks much like it did when built and is used to carry on even older traditions. The Troop’s monthly meetings, which operate under Robert’s Rules of Order, take place in the hall, as do inductions into the Troop and member promotions.

Fancy rooms, check. What else is inside?

The Troop's museum features artifacts from its history, including rifles, swords, and uniforms. Jared Whalen/Billy Penn

Artifacts not on display throughout the building are on display in the Troop’s museum, which contains pieces dating back to its formation. Rifles, sabers and uniforms revealing the chronological changes in the unit are on display throughout the gallery. While currently being held elsewhere, the museum also displays a hand-written letter from George Washington thanking the Troop for escorting him during the Revolutionary War.

One of the Armory’s most valued items is the Markoe Standard, a flag first used during the Troop’s escort of General Washington during his trip from Philadelphia to Boston to take command of the Army in 1775. The Troop went on to carry the standard throughout the Revolution.

The Markoe Standard represents the nation's attitude of unionization during the Revolution. Jared Whalen/Billy Penn

In addition to the flag’s significance in the Troop’s history, it also represents a dramatic shift for the country. The Markoe Standard is believed to be one of the first flags to use 13 alternating stripes as a representation of the unionization of the colonies.

“What you see here is a change in character,” Noyes said. “If you look very carefully behind these stripes, you can see what is left of a Union Jack. Around the country, we were using new motifs to show this union of colonies.”

Beyond the historical value of the artifacts, though, is what they represent to those still a part of the Troop. Unlike normal soldiers, the military is not their job, as any money they receive from the government goes back into the unit. For these men, though, the culture of being a part of First Troop is worth much more.

“You get the prestige, if you give it enough years, to be a part of something that’s incredibly special.” Noyes said. “It’s a fraternity for life. Our wives know each other. Our kids know each other. Our grandchildren know each other. It often becomes a family tradition. It’s almost like this close affinity and friendship and love that has permeated through the generations.”