$row_0 = array(1, 2, 3);
$row_1 = array(4, 5, 6);
$row_2 = array(7, 8, 9);
$multi = array($row_0, $row_1, $row_2);

You can refer to elements of multidimensional arrays by appending more []s:

$value = $multi[2][0];                 // row 2, column 0. $value = 7

echo("The value at row 2, column 0 is {$multi[2][0]}\n");

Failing to use the curly braces results in output like this:

The value at row 2, column 0 is Array[0]

5.3. Storing Data in Arrays		5.5. Extracting Multiple Values