Eugenio Barsanti and Felice Matteucci patent in 1854 in London (patent no. 1072) a gas engine that pushes a free piston through the explosion of a gas-air mixture, being the first documented internal combustion engine with a verifiable patent. They present an improved version in 1857 to the Accademia dei Georgofili in Florence. Nikolaus Otto, whose four-stroke engine (1876) would become the universal standard, visited Florence in 1867 and had documented access to the Italian technical literature of the period. There is no direct proof that Otto knew of Barsanti-Matteucci's work, so this entry uses 'silenced' rather than 'appropriated': the erasure was structural (the inventors died before commercializing it, the patent lapsed), not necessarily deliberate.