It’s funny where observation leads one - the Romans didn’t understand why salt water was good for sanitizing (that most microbes are not halophilic), but recognized by practice that it was good. There’s a bit in De Architectura where Vitruvius discusses how a town dug a channel from the sea to turn the nearby swamps into a brackish marsh, and that disease rates plummeted afterwards. If memory serves he attributes it to ‘poisonous vapors’ being removed by the saline water, while we would recognize it as destroying the ideal environment for mosquitos and other such insects.