Today in 1536, Florentine merchant Francesco Lapi used the @ sign for the first time in recorded history. Giorgio Stabile, a professor of the history of science at La Sapienza University, found the first known instance of its use in a letter written by Lapi on May 4, 1536. The @ sign represented an amphora, a measure of capacity based on the terracotta jars used to transport grain and liquid in the ancient Mediterranean world. Sent from Seville to Rome, the letter described the arrival in Spain of three ships bearing treasure from Latin America.
In late 1971, Ray Tomlinson used @ to distinguish local email from network email on the nascent Internet, to indicate that the user was “at” some other host rather than being local.
Daniel Soar observed in 2009 in the London Review of Books: “And now, of course, it’s ubiquitous. No one would know where anything was meant to go if it wasn’t for the amazing @…. Twitter, the social networking site that everyone is tweeting about, has been plotting the takeover of @ for a long time. … In email addresses, @ is all about precision and privacy: your message is routed to a particular individual at a particular domain, to a subset containing a single member. Twitter reverses the principle: it makes @ a tool for sending a message to an individual – @barackobama, @oprah, @therealdevil – that anyone who chooses to can overhear. The at sign used to indicate a whisper: now it’s become a gargantuan shout.”