As the entry point for nearly 12 million immigrants between 1892 and 1954, Ellis Island occupies an important place in our collective memory. Left vacant and untended for 30 years after the processing facility was closed, the island's main building was renovated and restored in the late 1980s, under the auspices of the National Park Service. Arching above the registry room is a magnificent vaulted masonry ceiling, 60 feet high, 190 feet long, and 102 feet wide. The ceiling consists of three layers of interlocking, 3/4-inch-thick terra cotta tiles set in a herring bone pattern in portland cement mortar. This technique is called Guastavino vaulting after its inventor.