“Likewise the weight of the walls should be relieved by arches of wedge-stones, their joints converging on a centre.”
The hint
An arch stands on nothing until the last stone is set, and then it stands on everything. Five by five. Row first, then column. The square remembers.
The cipher
25 · 15 · 54 · 43 · 44 · 34 · 33 · 15
— Vitruvius · De Architectura · c. 15 BCE
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