The Greek revival townhouses facing the private park in this tony square went up in the 1820s, 1830s, and 1840s. The square was exclusive then and it’s exclusive now.

But taking in the bow-fronted facades of its houses is absolutely free. The whole thing makes for a very pleasant stroll, though it might consume a good chunk of your two-hour tour of Beacon Hill architecture.

Built in 1808 and named after the historian who lived there in the mid-1800s, this mansion is from the hand of Asher Benjamin, who would end his career working in the Greek revival style.

This is a federal work, though through the pilasters and the Doric columns you can almost see a more vigorous approach yearning to show itself.

It’s now a museum that the National Society of the Colonial Dames of America runs. (Bonus federal: Benjamin also designed 54 Beacon.)

Asher Benjamin, a pioneer in the federal and Greek revival styles, designed this building, which went up in 1806 and remains the oldest African-American church building in the U.S.

Not surprisingly, the building served as a hotbed of abolitionism in the early 1800s, and became a synagogue in the 20th century.

The Museum of African American History purchased it in the 1970s, and it remains a part of that institution.

Another Asher Benjamin creation, the Old West Church was originally erected in 1806 for a Congregational parish whose church the British destroyed during the Revolutionary War. (The redcoats thought that colonial troops were using the steeple to signal their compatriots in Cambridge.)

After a century and half, it became a branch of the Boston Public Library and has been a Methodist parish since the early 1960s.

The State House was finished in early 1798 and built on a cow pasture John Hancock once owned. Charles Bulfinch, the first American architect to achieve wide fame, designed it.

It is a particularly prominent example of the U.S.-born federal style.

A builder named Thomas Fletcher constructed this four-story rowhouse in 1808. Various owners renovated it throughout the 19th century, including painter Chester Harding, who lived there in the late 1820s.

The Unitarian Church Association acquired 16 Beacon Street in the 1920s, and adapted the house for use as an office. In 1963, the Boston Bar Association moved in, and renovated it some more (the group still owns the property).

Yet its facade especially retains the trappings of that federal style.