Reversing string in php

<?php
function reverseString($string){
    $to_return = '';
    $chars = str_split($string);
    $ln = count($chars);
    for($i =  $ln - 1; $i>=0; $i--){
    $to_return .= $chars[$i];
    }
    return $to_return;
}

echo reverseString("Hello World");