The Basilica has welcomed millions of visitors, including Pope John Paul II in 1995, Mother Teresa in 1996, and Ecumenical Patriarch Bartholomew I of Constantinople in 1997. The building has also been visited by at least 20 other saints or potential saints. The Cathedral is a monumental neoclassical-style building designed in conformity to a Latin cross basilica plan — a departure on Latrobe's part from previous American church architecture, but in keeping with longstanding European traditions of cathedral design. The plan unites two distinct elements: a longitudinal axis and a domed space. The main façade is a classical Greek portico with Ionic columns arranged in double hexastyle pattern, immediately behind which rise a pair of cylindrical towers. Architectural historian Henry-Russell Hitchcock believed that the onion-shaped domes atop the two towers were “not of Latrobe's design,” but now it is believed that they "were entirely the architect's own." The exterior walls are constructed of silver-gray gneiss quarried from the Ellicott City Granodiorite. Latrobe originally planned a masonry dome with a lantern on top, but his friend Thomas Jefferson suggested a wooden double-shell dome (of a type pioneered by French master builder Philibert Delorme) with 24 half-visible skylights. For the inner dome Latrobe created a solid, classically detailed masonry hemisphere. Grids of plaster rosettes adorn its coffered ceiling. The interior is occupied by a massive dome at the crossing of the Latin cross plan, creating a centralizing effect which contrasts the exterior impression of a linear or oblong building. Surrounding the main dome is a sophisticated system of barrel vaults and shallow, saucer-like secondary domes. The light-filled interior designed by Latrobe was striking in contrast to the dark, cavernous recesses of traditional Gothic cathedrals. The Basilica houses many precious works of art, including two heroic portraits: the first entitled "Descent from the Cross" by Pierre-Narcisse Guérin and the second, by Baron Charles de Steuben, depicts Louis IX of France burying his plague-stricken troops before the siege of Tunis at the beginning of the Eighth Crusade in 1270. Both portraits were gifts of King Louis XVIII of France shortly after the 1821 opening of the Basilica. A 32-month, $34 million restoration project was completed in 2006. The restoration included a total incorporation of modern systems throughout the building, while also restoring the interior to Latrobe's original design.