bene noverit orbem
fluminaque et portus, mundum ventosque, necesse est
iamque huc atque illuc agilem convertere clavum
et frenare ratem fluctusque effundere rector,
iam remis agere et lentas inflectere tonsas.
‘The pilot must have sound knowledge of the earth, its rivers and havens, its climate and winds; how on the one hand to ply the mobile helm this way and that, and brake the ship and spread apart the waves, and how on the other to drive the ship by rowing and to feather the lingering blades.’