The most important of Taj Mahal attractions is of course the Mausoleum. The dome above the tomb is referred to as an onion, given its shape. The columns are an important feature of its design as they allow for light to penetrate the interior. The exterior décor is said to be an exemplary show of Mughal design. The Mughal Empire was the longest period of prosperity which lasted from the 1500s through the middle of the 19th century.