Clairvaux, known scientifically as Trappist-1e, is the fourth planet in the Trappist-1 system, and among the earliest human exoplanetary colonies. A readily-habitable garden world, Clairvaux has played host to a rich native ecology and a developed human settler population. First discovered in the early 21st century, Clairvaux and its sister planets Dijon (Trappist-1d), Bernard (Trappist-1f), and Cassino (Trappist-1g) were understood to have liquid water, amenable temperatures, and exist in the habitable zone of its parent star, the cool red dwarf star Trappist-1. Existing only 40 light years away from Earth, the system was "so close to feel, too close to touch" for the first century of extrasolar colonization. But the production of Jump Lane Developers allowed rapid expansion, and a settlement was established on Trappist-1e in 2313.

Clairvaux became the most densely populated, but it learned the lessons of the Tau Ceti crises of the late 23rd centuries and developed with an appreciation for the native biosphere. Due its relative position, Clairvaux largely evaded the tumult of the Orion revolutionary activity in the 24th century. The Trappist-1 system as a whole was admitted as a member state of the Terran Federation in 2396, incorporated as the La Trappe Union. The system was administered as a province of the Terran Empire until the reorganizations of the 2900s, when it was reformed as a county. After the dissolution of the Empire and the formation of the CGU, Clairvaux gained independence as a member world, administered as the Principality of Clairvaux. The incumbent and 35th Count of Clairvaux, Julien III de Batz, was declared Sovereign Prince of Clairvaux as head of state and government, and was created a prince in the peerage of the Republic with the same title.

Since its earliest settlement, the worlds of the Trappist-1 system have had a high proportion of traditionalist Roman Catholics among its population, and many of its oldest settlements were founded as Catholic monasteries and missions. Clairvaux notably contains the second largest number of abbeys and monasteries in the Inner Sphere, next only to Earth itself. Catholic clergy have historically held considerable political and economic power in the Trappist colonies. Secularization was a sluggish, fraught process that only occurred in the Terran Imperial period, after four centuries of clerical influence. Controversially, the recent princely government has allowed some political autonomy to the monasteries and has appointed the planetary Archbishop to a position in the executive council.

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