An 'unbreakable' beam bridge and a hundred-mile acoustic relay
A double-deck bridge of chained master beams, and news relayed through underground conduits
Bridge and communication studies. Two drawings show a timber bridge, the central one described as 'unbreakable' if its master beams a b and c d are strong and well chained together, and able to carry two decks, one above the other. A separate note proposes a relay of a hundred houses over a hundred miles, each with guards, through whose underground conduits a piece of news can be heard within a quarter of an hour.
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Timber bridge for construction
The uppermost drawing is a study for the construction of a bridge, framed by diagonal braces. It leads into the more finished central design.
Unbreakable double-deck bridge (a b, c d)
The central bridge is called unbreakable provided its master beams a b and c d are strong and well chained together. Leonardo adds that it could carry two passages, one above and the other below.
Relaying news through underground conduits
A note proposes a hundred houses set over a hundred miles, each holding guards, so that through underground conduits a piece of news can be heard within a quarter of an hour. It is an acoustic relay spanning a whole territory.