Wallis' Sheldonian theatre roof

The roof of the Sheldonian theatre in Oxford, built from 1664 to 1669, is constructed from timber beams which are unsupported apart from at the walls, and held together only by gravity.

The [design of the roof was due to John Wallis](https://www.soue.org.uk/souenews/issue4/wallis.html), the Savilian Professor of Geometry.

"So effective [was the roof] that for nearly a century the University Press stored its books ..., and for many years it was the largest unsupported floor in existence"