You use it every single day. In English it's called the "at sign." The Italians call it "snail." The Spaniards, "arroba." The Slavs, "monkey." But what did @ really mean 473 years ago?
On May 4, 1536, Francesco Lapi—a Florentine merchant who at the time was in Seville, Spain—used the symbol @ in a letter, the first ever known instance of a document containing it. It didn't had a domain name after it, however. Back then, he was referring to the number of "amphoras" that were shipped in three vessels which departed Spain on their way to Rome, Italy. An "amphora" was a commercial volume measure of those times. The document you can see above says:
There, an amphora of wine, which is one thirtieth of a barrel, is worth 70 or 80 ducats.
In Spanish, the word for that measure was called "arroba," which is the name the @ symbol still receives today in that language. Later, the symbol was conserved in typewriters' keyboards: People kept using the at sign through the centuries, and it was common in commercial accounting where it meant "at the price of."
It was in 1971 when Ray Tomlinson saw the symbol and thought it could be good to append the mail server host to the name of the person receiving an email:
I chose to append an at sign and the host name to the user's (login) name. I am frequently asked why I chose the at sign, but the at sign just makes sense. The purpose of the at sign (in English) was to indicate a unit price (for example, 10 items @ $1.95). I used the at sign to indicate that the user was "at" some other host rather than being local.
And the rest, as they say, it's history. I don't know about you, but from now on I would be saying jesus amphora gizmodo dot com every time I have to tell my mail address. It just sounds so much better. Or better yet, jesus monkey gizmodo dot com. Yes. Definitely this one. [NYT Blog]