▲As an architect's tools, the square and compass are used in Masonic ritual as emblems to teach symbolic lessons. 'Duncan's Masonic Monitor,' published in 1866, explains them as: "The square, to square our actions; The compasses, to circumscribe and keep us within bounds with all mankind."

▲The concept of God as the Great Architect of the Universe is embraced within Freemasonry because science, and particularly geometry and astronomy, was linked to the divine for most medieval scholars.

▲Another iconic symbolic emblem of Freemasonry is the apron. It's the unique badge of a Mason and considered a tool. Pictured is Voltaire's Masonic apron from 1778.

▲The single most identifiable symbol of Freemasonry, a compass and square represent the convergence of matter and spirit.

▲The French Museum of Freemasonry in Paris chronicles the history of French Freemasonry through its symbols, grades, documents, and objects.

▲Pictured is a selection of historic tools exhibited at the museum, just some of the approximately 10,000 items displayed in permanent exhibit space.

▲A ceremonial throne made for the Prince of Wales (later King George IV) in 1790. The gilded limewood chair features Masonic symbolism, including astronomic globes and square and compass.

▲One of the most important Masonic temples in Spain, the building's edifice is distinguished by strong symbolism, most of which was inspired by the architectural tradition of ancient Egypt.

▲A teaching aid used by experienced members during lectures, tracing boards are painted or printed illustrations depicting the various emblems and symbols of Freemasonry. Pictured is an example dating back to 1876.

▲For centuries, Masons used various signs (hand gestures), grips, or "tokens" (handshakes) to identify legitimate Masonic visitors from non-Masons. Pictured is a bas-relief with a Masonic handshake, located on the front of a house on Fontanka Embankment in Saint Petersburg, Russia.

▲A Masonic jewel made by a French prisoner of war during the Napoleonic Wars displays Freemasonry's most potent symbols.

▲Masonic jewels, or badges, are the earliest surviving objects of Freemasonry. These badges are classified as jewels because they have an ethical and honorable propensity that makes them gems of immeasurable value.

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Edited by Presbyterian clergyman James Anderson, 'The Constitutions of the Free-Masons,' published in 1723, sets out the general code of conduct expected from all Freemasons, as well as specific rules by which a Grand Lodge and the lodges under its control are to be governed.

▲The Masonic apron was developed from the lambskin apron worn by operative stone masons in the Middle Ages. It symbolizes hard work, regeneration, or a new life. It also refers to the "pure heart."

▲There are several variations of handshakes, including the 'Master Grip,' 'Real Grip of Fellow Craft,' and 'Grip of the Entered Apprentice.'

▲Masonic gloves symbolize the 'Works of the Hands.' The acts of a Mason should be as pure and as spotless as the gloves they wear. The gavel is an emblem of authority used by the Master of the lodge.

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Although originally a Christian symbol, the Eye of Providence is often associated with Freemasonry. It represents the eye of God watching over humanity (the concept of divine providence).

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The checkerboard carpet, or mosaic pavement, represents the ground floor of King Solomon's Temple and is "emblematic of human life, checkered with good and evil."

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A rough and perfect ashlar is a stone that symbolizes man's moral and spiritual life. Pictured is a rough ashlar before it's been shaped and finished (a perfect ashlar) for its place in a wall.

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King Solomon's Temple is a central symbol of Freemasonry. The first three Grand Masters were King Solomon, King Hiram I of Tyre, and Hiram Abiff—the craftsman/architect who built the temple. Ritual objects representing the architecture of the temple include the pillars Boaz and Jachin, which stood at the temple's entrance.

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The abiding relationship between ancient astronomy, religion, and Freemasonry is reflected in many famous structures of archaeological significance around the world. The stone circle of Stonehenge and the great pyramids of Egypt are excellent examples.

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One of the most important symbols of Freemasonry, crossed keys is the sign of the treasurer of a Lodge and, in general, secrecy: it's a reminder that the secrets of Freemasonry are to be locked up or concealed in the heart.

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A compass and square with the letter "G" in the center can stand for Geometry, the "noblest of sciences," or Great Architect of the Universe.

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In this mosaic frieze, the pillars Boaz and Jachin flank the Ark of the Covenant with Jacob's Ladder stretching towards the Hebrew character Yod (for Jehovah). On the ladder are the Volume of the Sacred Law and the symbols for faith (cross), hope (anchor) and charity (burning heart). King Solomon and Hiram Abiff stand on the sides.

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Pictured is the House of the Temple in Washington, D.C. This historic structure illustrates the remarkable wisdom of the ancient astronomers and the capabilities of the Freemasons, who converted abstract religious concepts into grandiose monuments to reflect those concepts.

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This hall in London has been a Masonic meeting place since 1775. It features an impressive mosaic ceiling decorated with figures and symbols from Masonic rituals.

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Pictured is a late 19th-century bejeweled badge made to commemorate Queen Victoria's Diamond Jubilee.

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Jacob's Ladder is the portal by which Masons are able to ascend to the summit of masonry. It's the ladder leading to heaven that was featured in a dream the biblical Patriarch Jacob had during his flight from his brother Esau in the Book of Genesis.

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Ancient rituals, odd-looking emblems, hidden handshakes. Freemasonry—the world's oldest fraternal organization—is wrapped in mystery and intrigue. But what exactly does all that symbolism mean, and where did it come from?

Browse this gallery and peek inside the secretive world of the Masons.