The building of La Mezquite, Cordoba's grand mosque-turned-cathedral, was begun in the year of 785. Under the rule of Abd al Rahman I, Andalucia's first Moorish king, the original mosque was deemed complete by the year 787. It continued, however, to be improved over the centuries with such additions as an elaborate Mihrab or prayer niche and a royal enclosure for the caliphs.
Inside of this awesome structure is a forest of over 850 columns which were "recycled" from abandoned Roman and Visigothic temples. This building was quite literally pieced together like a quilt! Atop these ancient columns rest two layers of gigantic candycane-striped arches which make for a glorious visual effect.
La Mezquite is sometimes refered to as the upside-down building because the majority of its weight is on the top. In the 16th century, after the expulsion of the Moors, many of the central arches and supports were torn out. This was done to make room for a new cathedral. It was, of course, a major weakening of the structure which (from a technical standpoint) should have collapsed.
After 750 years of being in operation as a cathedral, all of Spain still refers to it as La Mezquite or even Mezquita. Perhaps this is done out of a sheer admiration for the Moors who designed such an engineering marvel: A building that shouldn't be able to stand at all -- yet does so solidly.