The sides of this nest should be packed hard, the bottom smooth and slightly Concaved, not too much, as the tendency then would be to break the eggs if they crowded towards the centre.
"Natural and Artificial Duck Culture"
James Rankin
Onely there is this remedie, to fill the diche: the whiche is moste difficulte to dooe, as well bicause the capacitie thereof is greate, as also for the difficultie, that is in commyng nere it, the walle beeyng strong and Concaved, betwene the whiche, by the reasons aforesaied, with difficultie maie be entered, havyng after to goe up a breache through a ruin, whiche giveth thee moste greate difficultie, so that I suppose a citee thus builded, to be altogether invinsible.
"Machiavelli, Volume I The Art of War; and The Prince"
Niccolò Machiavelli
San Francisco's magnificent municipal building had Concaved like an egg shell.
"Complete Story of the San Francisco Horror"
Richard Linthicum Trumbull White Samuel Fallows