The equals sign was invented in the 16th century

Explanation

It was introduced in 1557 by the Welsh mathematician Robert Recorde in his book "The Whetstone of Witte", because he was tired of writing "is equal to" over and over. He chose a pair of parallel horizontal lines of equal length since, in his words, "no two things can be more equal" (originally spelled "no 2 thynges can be moare equalle"). The symbol still took centuries to catch on, other mathematicians kept using their own alternatives long after his death, and Recorde never got to enjoy the success since he died in a London debtors' prison the very next year, in 1558.