upon what grounds

And this night, I know not upon what ground, the gates of the City [were] ordered to be all shut, and double guards everywhere, and we are going upon making of all ships coming from thence and Hambrough, or any other infected places, to perform their Quarantine (for thirty days as Sir Rd. Browne expressed it in the order of the Council, contrary to the import of the word, though in general acceptation it signifies now the thing, not the time spent in doing it) in Holehaven, a thing never done by us before.