In order to send secure messages to his generals on the battle field, Julius Caesar created a very simple method of encrypting his communications.

"If he had anything confidential to say, he wrote it in cipher, that is, by so changing the order of the letters of the alphabet, that not a word could be made out. If anyone wishes to decipher these, and get at their meaning, he must substitute the fourth letter of the alphabet, namely D, for A, and so with the others."
— Suetonius, Life of Julius Caesar

A Caesar shift of 13 is also performed in the ROT13 algorithm.

Below, is a little program I wrote which will convert text to or from the Caesar shift cipher.  Feel free to enter any words you'd like. This program will handle English, German and Spanish text. Just make sure to either select "English" , "Deutsch", or "Español"  in the drop-down menu below.