The Ottoman threat compelled Venice to undertake the first significant enhancements of the city’s old fortifications. Along the southern front, an inclined bulwark (scarpa) was added, founded within the moat and buttressed against the inner curtain wall by vertical counterforts (speroni) bridged with vaults and filled with compacted earth. In practice, the old and new fortifications functioned as a single defensive line. Work on strengthening the fortifications began in 1472 and was not fully completed until 1525. During this period, the central southern gate—known in contemporary sources as the Portone, and later as the Voltone— was remodelled.