Try to think of how many times each day you use the '@' symbol. So far this morning (and it's only just past 9am) I've used it six times in emails and tweets.
The ubiquity of the "at symbol" (also called the "snail" by Italians and the "monkey" in Slavic languages) would makes us think it's a 20th century phenomenon.
But we would be wrong. In fact, a recently discovered letter by a Florentine merchant named Francesco Lapi used the symbol @ in a letter written exactly 473 years ago, on May 4, 1536.