De parasito sive artem esse parasiticam

Lucian of Samosata

Lucian, Vol. 3. Harmon, A. M., editor. London: William Heinemann, Ltd.; Cambridge, MA: Harvard University Press, 1921.

Reflect, too, that we cannot exercise the other arts

v.3.p.269

while on a journey or a voyage, but this one can be plied both on the road and at sea.