Horseback
From Letter To Thomas Moore by Erasmus

The references to idleness and writing on horseback, like the date-line 'from the country', should not be taken literally. They are conventional scholarly disclaimers, like that of Petrarch who claimed to have written his own discourse on his ignorance on a boat, or that of More who had claimed to have composed his Utopia at odd moments. These are conventional warnings that we should not regard the ensuing work as totally serious.