The origin of juggling lays far back in ancient history. As a close relative to dance, music and theatre performance arts, juggling has been around for ages, literally.
Pinpointing the start of juggling is futile and anyone who attempts is doomed to fail.
Some historians believe that juggling has been part of religious expression since the dawn of time, then designed to rid the shamans' tribes of evil spirits.
The first pictures of jugglers appear in egyptian wall paintings and Greek vases. The first date we have regarding juggling is in the time around 700 BCE, linked to events in ancient greek history, in that jugglers were "imported" from oriental countries.
The name Juggling
Some Latin scholars note that the latin word for juggler was ventilator, or thrower of knives, and attribute the word juggler to this. Far from everybody agrees however.
The general idea is that Juggling was such a strange thing, that there was no word for it - and chances are that jugglers were called "throwers of things".
A Jaculator (yes, same word base as ejaculation, without further connection) is means "thrower", and the most likely explanation as to where the word juggle came from.
From the word joculator (Joker or jester), the French came up with Joglar, which later became jongleur.
The spanish use the word malabarista, which is a bit of a mysterium. :)