Origins
The word 'fortress' is built on strength β literally.βββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ It descends from Latin 'fortis' (strong, brave, robust), one of the most prolific adjectives in the Latin vocabulary, and its English descendants form a family so large that most speakers never realize how closely related words like 'fortress,' 'comfort,' and 'effort' truly are.
'Fortress' entered English in the fourteenth century from Old French 'forteresse,' meaning a strong place or stronghold. The Old French word derived from Vulgar Latin forms related to 'fortis,' with the suffix '-itia' (forming abstract nouns) producing something like *fortalitia β a fortification, a place characterized by strength.
Latin 'fortis' itself has a debated Proto-Indo-European ancestry. The most widely accepted reconstruction links it to *dΚ°erΗ΅Κ°- (to hold firmly, to be strong), though some scholars connect it to *bΚ°erΗ΅Κ°- (high, elevated), which would link 'fortress' to 'berg' (mountain) and 'borough' through Germanic. The uncertainty is typical of reconstructions at such chronological depth.
Development
The family of English words descended from 'fortis' is remarkable for its range:
'Fort' β the most direct descendant, borrowed from French, a fortified military installation. 'Fortify' β from Latin 'fortificΔre' (to make strong), from 'fortis' + 'facere' (to make). 'Fortitude' β from Latin 'fortitΕ«dΕ' (strength, courage), the moral equivalent of physical strength. 'Forte' β from Italian 'forte' (strong), used in English both for a person's strong point and as a musical direction meaning 'loud' (since volume is the strength of sound). 'Force' β from Vulgar Latin *fortia (strength), the noun form of the adjective.
'Comfort' β perhaps the most surprising member of the family. It comes from Old French 'conforter,' from Late Latin 'confortΔre,' meaning 'to strengthen greatly.' The prefix 'con-' (together, with) here functions as an intensifier. To comfort someone was originally to give them strength, to fortify them against grief or hardship. The modern sense of 'ease, consolation, physical ease' is a softening of the original meaning, but the etymology reveals that comfort was once understood as an active, strengthening force, not passive coziness.
Proto-Indo-European Roots
'Effort' β from Old French 'esfort,' from Vulgar Latin *exfortia, literally 'a putting forth of strength' (ex- = out + fortis = strong). When you make an effort, you are etymologically pushing strength outward.
In the military and architectural sense, a fortress represents the ultimate expression of the concept embedded in its root. The great fortresses of history β the Krak des Chevaliers in Syria, the Tower of London, the ChΓ’teau de Carcassonne β were designed to be so strong that they could not be taken by force (itself a 'fortis' word). The redundancy is telling: a fortress resists force because both words mean the same thing. The architecture of strength described by its own name.