How to play Roman numerals on Apple's mobile phone?

The method of inputting Roman numerals on Apple's mobile phone is as follows:

First, open any input box, such as SMS or email. Then, enter the numeric keyboard interface, click the "123" button and switch to the symbol keyboard. You can find many special characters and symbols by sliding on the symbol keyboard. Find the location of Roman numerals: you can slide to the left on the keyboard, or click the #+= button and then click the "123" button to see Roman numerals such as "I", "II" and "III". Click on the desired Roman numeral to insert it into the input box.