The Etymology of Firewall
The firewall was physical before it was digital. After the Great Fire of London in 1666, building regulations began requiring non-combustible party walls between adjoining properties — barriers that would stop fire spreading from one section to the next. The compound 'firewall' became standard architectural terminology. In 1988, network security researchers borrowed the metaphor for a system that controls traffic between trusted and untrusted networks, and it became one of computing's most successful analogies. Each language independently built its own compound: German 'Brandmauer,' French 'pare-feu,' Spanish 'cortafuegos.' The metaphor succeeds because the function is identical: controlled passage in normal conditions, absolute barrier when threat arrives.