A familiar cross became a distinct arithmetic mark
The multiplication sign × is a plus sign’s strokes turned diagonally. That simple change makes two operations that both combine quantities easier to tell apart on the page: + keeps one stroke upright and the other horizontal, while × sets both at an angle.
The mark entered European mathematical notation in the 17th century, when printed symbols were helping arithmetic become easier to record and teach. English mathematician William Oughtred used × in his 1631 book Clavis Mathematicae. Its shape was easy to recognize and reproduce, even before multiplication notation had settled into the forms familiar today.
Why the sign is not always an X
The mark resembles the letter x, but in arithmetic it has a specific job: in 3 × 4, it tells the reader to multiply 3 by 4. That resemblance can cause confusion in algebra, where x often stands for an unknown number. For that reason, mathematicians also write multiplication as a centered dot, as in 3 · 4, or leave it implicit in expressions such as 3(4).
The diagonal cross remains especially useful in elementary arithmetic, where it makes the operation unmistakable at a glance. A small turn of the strokes separates multiplication from addition without needing a new shape altogether.
