Europeans in the 16th century divided the world into four continents: Africa, America, Asia and Europe.
if you see all continents had same first and last letter. like AsiA have same “A” , start and last character.
suppose AmericA has common “A” for first and last character. and same for AsiA had common “A” for first and last letter. and last not least EuropE had “E” common for first and last letter.