Grande complication pocket watch · France

Leroy 01

Partially verified

Commissioned by the Portuguese collector Antonio Augusto de Carvalho Monteiro with instructions to combine everything then achievable in watchmaking science and mechanics, the Leroy 01 held a long-standing reputation, repeated in specialist literature, as the most complicated watch in the world for roughly eight decades after its completion. [1](http://www.mdt.besancon.fr/wp-content/uploads/2014/07/La-Leroy-01_fiche-%C3%A9l%C3%A8ve.pdf)

Technical facts

Complications: 24 functions across two dials, including a perpetual calendar, grande and petite sonnerie, minute repeater, times in 125 cities, sunrise/sunset, equinoxes and solstices, and interchangeable celestial charts
Case: 18-carat gold, approximately 71 mm diameter
Movement: Reported to comprise 975 individual parts

Historical significance

Commissioned by the Portuguese collector Antonio Augusto de Carvalho Monteiro with instructions to combine everything then achievable in watchmaking science and mechanics, the Leroy 01 held a long-standing reputation, repeated in specialist literature, as the most complicated watch in the world for roughly eight decades after its completion. [1](http://www.mdt.besancon.fr/wp-content/uploads/2014/07/La-Leroy-01_fiche-%C3%A9l%C3%A8ve.pdf)
The watch has two dials (one on each face) carrying 24 functions in total, including a display of the time in 125 cities, a perpetual calendar, and interchangeable star charts, contained within a 71 mm case — an unusually large but still pocket-portable form for the number of functions included. [1](http://www.mdt.besancon.fr/wp-content/uploads/2014/07/La-Leroy-01_fiche-%C3%A9l%C3%A8ve.pdf)
Remained in the Carvalho Monteiro family until 1953, when it was acquired by public subscription for the city of Besançon's museum; researchers should treat claims about its 'most complicated' status as a period and specialist-literature characterisation rather than a fixed, permanently unchallengeable record, since later watches (including modern grande complications) have since matched or exceeded its complication count by some counts.

Background

The Leroy 01, also known as Lucie, was created by the Paris-based firm L. Leroy & Cie as a unique masterpiece of luxury watchmaking and goldsmithing. It was commissioned in 1897 by the wealthy Portuguese collector António Augusto Carvalho Monteiro, who requested a timepiece that combined all scientific and mechanical capabilities of the era. The watch was assembled in the company's workshops in Besançon, requiring seven years of intensive expert labor between 1897 and 1904. The instrument was honored with a special grand prize from the jury at the 1900 Universal Exhibition in Paris.

Written from the encyclopedia entries listed under Sources; each statement was checked against the cited text. Passages from sources in other languages are given in English translation.

Construction and mechanism

The watch features an 18-carat chiseled gold case with a diameter of 71 mm and weighs 228 grams.
Its mechanical movement is comprised of 975 individual parts assembled across four distinct layers.
The timepiece displays 24 complications across two dials, including a perpetual calendar, astronomical data, and various environmental sensors.

Later history

The watch remained with the descendant family until 1953, when it was offered for sale.
It was acquired through a national subscription campaign in 1957 and subsequently moved to the collections in Besançon.
The watch is currently exhibited at the Musée du Temps in Besançon, which opened in 2002.

Castres - Hôtel Leroy 01 — Tylwyth Eldar, CC BY-SA 4.0. Wikimedia Commons file page

Sources & references

Leroy 01, Wikipedia (French), retrieved 2026-10-28 (text CC BY-SA 4.0)
Musée du Temps, Besançon, published catalogue materials on the Leroy 01
hautehorlogerie.org, Fondation de la Haute Horlogerie, encyclopedia entry on Louis Leroy

Where sources disagree, the disagreement is stated rather than resolved silently.