Horizon

But what is an "aphorism"? 

The root of the word is the same as "horizon". The Greek verb "horizo" means "to delimit". Horizon is originally the circle that opens to the eye. 

Francesco da Buti, Dante's fourteenth-century commentator, offers us a precise definition: "The horizon is the terminative circle of our view". 

No less precise is Italian Poet Tasso in the "Created World": "What human sight ended / in the dark and lucid borders/horizon was said".