The marble floor of the Great Hall contains a number of modeled and incised brass inlays. The center represents the Sun, on which are noted the four cardinal points of the compass, indicating the main axes of the building. A decorative scale pattern encloses the Sun with alternate sections of red and yellow Italian marble, the former from Verona and the latter from Sienna.

Twelve squares at the perimeter of the floor of the Great Hall represent the signs of the zodiac. The other squares form two patterns of rosettes. They are embedded in blocks of dark red, richly mottled French marble, with borders of pure white Italian marble.

Proceeding clockwise from bottom left, the zodiac signs are Leo, Cancer, Gemini, Taurus, Aries, Pisces, Aquarius, Capricorn, Sagittarius, Scorpio, Libra, and Virgo.

This Commemorative arch by Olin L. Warner (1844–1896) leading to the Main Reading Room commemorates the erection of the Library of Congress. Its sculpture The Students represents the pursuit of knowledge. On the left a young man seeks knowledge through reading. On the right an older man with flowing beard is shown absorbed in meditation, no longer concerned so much with a source of learning because he observes life and engages in original reflection and thought.

In the frieze above them the words “Library of Congress,” are inscribed in tall gilt letters.

A second inscription names those involved in the building of the Library. The text reads:

Erected Under the Acts of Congress of
April 15, 1886; October 2, 1888; and March 2, 1889 by
Brig. Gen. Thos. Lincoln Casey
Chief of Engineers U.S.A.

• Bernard R. Green Supt. and Engineer
• John L. Smithmeyer Architect
• Paul J. Pelz Architect
• Edward Pearce Casey Architect

The numerous representations of eagles throughout the building are symbols of the federal government.

Presiding over the Library of Congress from a central position is Minerva, the Roman Goddess of learning and wisdom. In this mosaic by Elihu Vedder (1836–1923), she is portrayed as the Minerva of Peace and appears as the guardian of civilization with her armor partly laid aside.

Her attention is directed to an unfolded scroll that she holds in her left hand on which is written a list of various fields of learning, such as Architecture, Law, Statistics, Sociology, Botany, Biography, Mechanics, Philosophy, Zoology, etc.

A small statue of Nike, a representation of victory or achievement, similar to those erected by ancient the Greeks to commemorate success in battle, stands next to Minerva. The figure is a winged female standing on a globe and holding out a laurel wreath (victory) and palm branch (peace) to the victors.

On Minerva’s right is an owl, symbolizing wisdom, perched upon the post of a low parapet.

In the sky the clouds of disaster and discouragement are rolled away, and the sun begins to emerge.

Although Minerva’s shield and helmet have been laid upon the ground, the goddess still holds a long, two-headed spear, showing that she never relaxes her vigilance.

Beneath the mosaic is an inscription from Ars Poetica by Horace (65–8 B.C.): “Nil invita Minerva, quae monumentum aere perennius exegit,” (Not unwilling, Minerva raises a monument more lasting than bronze).

The names and quotes in the Great Hall were chosen by Librarian of Congress Ainsworth Rand Spofford (1825–1908) and Charles W. Eliot (1834–1926), president of Harvard University.). The works of these illustrious authors were popular at the time the building was constructed, and they were considered to have made great contributions to literature and the study of history.

• Miguel de Cervantes Saavedra
(1547—1616), Spanish Writer

• Victor Hugo
(1802—1885), French Poet and Novelist

• Walter Scott
(1771—1832), Scottish novelist and poet

• James Fenimore Cooper
(1791—1851), American Novelist

Printers’ marks were a type of self-protection similar to a trademark or copyright today. Sometimes they stood for protected privileges granted by kings or religious leaders. Often they incorporated mottoes and were based on the names of kings or religious leaders. Mottoes were often in Latin and sometimes in Greek or Hebrew. There are fifty-six printers’ marks around the ceiling on this level.

— Johann Rosenbach

At the corners of the ceiling two winged figures of genius flank an emblem showing the traditional symbols of learning, a torch and a book. The figures were modeled by sculptor Philip Martiny (1858–1927). Stars appear in the painted background by the artist Frederic C. Martin (1866–?).

During the renovation of the Jefferson Building in the 1980s, restorers discovered that the metallic ornamentation of the ceiling, once thought to be silver leaf, is actually aluminum leaf. When the building was being constructed during the 1890s, aluminum was more precious than silver. The scale-pattern design of the six large skylights mirrors the pattern of the marble flooring beneath.