The Celtic hillfort of Otzenhausen is one of the biggest fortifications the Celts ever constructed. It was built by Gauls of the Treveri tribe, who lived in the region north of the fort. The first fortification was constructed in the 5th or 4th century BC, but the real heyday of construction dates to the 2nd and 1st century BC. For reasons yet unknown, the fort was abandoned shortly after this expansion.
The site is formed in the shape of a triangle with rounded ends. One rampart surrounds the whole fort. On the southern side, another similar embankment is built about 40 metres in front of the main one. The ends of this outer rampart approach the main one but do not touch it. Because the entrance of the main rampart is located on the western side, no significant purpose for the outer one has been determined. From west to east the fort extends 460 m, from north to south 647 m. The total length of the ramparts is 2500 metres and they contain 240,000 cubic metres of stone. Thousands of beams were attached to the ramparts which, as the diagram shows, probably presented a vertical stone wall to the exterior. Perhaps there was a second gate on the eastern side, but its existence is not yet proven.
In Roman time a small temple of 2.15 metres x 2.70 metres, dating from the 2nd or 3rd century A.D. was built of quartzite rubble stone and brick-shaped sandstone. When German tribes invaded the Roman territories in 4th century A.D, the fort was used again. During the Thirty Years War (1618–1648) the citizens of the surrounding villages again took refuge in the remains of the Celtic fort. Excavations took place in 1883 and from 1936 to 1939.References:
The Mosque–Cathedral of Córdoba, also known as the Great Mosque of Córdoba and the Mezquita is regarded as one of the most accomplished monuments of Moorish architecture.
According to a traditional account, a small Visigoth church, the Catholic Basilica of Saint Vincent of Lérins, originally stood on the site. In 784 Abd al-Rahman I ordered construction of the Great Mosque, which was considerably expanded by later Muslim rulers. The mosque underwent numerous subsequent changes: Abd al-Rahman II ordered a new minaret, while in 961 Al-Hakam II enlarged the building and enriched the Mihrab. The last of such reforms was carried out by Almanzor in 987. It was connected to the Caliph"s palace by a raised walkway, mosques within the palaces being the tradition for previous Islamic rulers – as well as Christian Kings who built their palaces adjacent to churches. The Mezquita reached its current dimensions in 987 with the completion of the outer naves and courtyard.
In 1236, Córdoba was conquered by King Ferdinand III of Castile, and the centre of the mosque was converted into a Catholic cathedral. Alfonso X oversaw the construction of the Villaviciosa Chapel and the Royal Chapel within the mosque. The kings who followed added further Christian features, such as King Henry II rebuilding the chapel in the 14th century. The minaret of the mosque was also converted to the bell tower of the cathedral. It was adorned with Santiago de Compostela"s captured cathedral bells. Following a windstorm in 1589, the former minaret was further reinforced by encasing it within a new structure.
The most significant alteration was the building of a Renaissance cathedral nave in the middle of the expansive structure. The insertion was constructed by permission of Charles V, king of Castile and Aragon. Artisans and architects continued to add to the existing structure until the late 18th century.
The building"s floor plan is seen to be parallel to some of the earliest mosques built from the very beginning of Islam. It had a rectangular prayer hall with aisles arranged perpendicular to the qibla, the direction towards which Muslims pray. The prayer hall was large and flat, with timber ceilings held up by arches of horseshoe-like appearance.
In planning the mosque, the architects incorporated a number of Roman columns with choice capitals. Some of the columns were already in the Gothic structure; others were sent from various regions of Iberia as presents from the governors of provinces. Ivory, jasper, porphyry, gold, silver, copper, and brass were used in the decorations. Marvellous mosaics and azulejos were designed. Later, the immense temple embodied all the styles of Morisco architecture into one composition.
The building is most notable for its arcaded hypostyle hall, with 856 columns of jasper, onyx, marble, granite and porphyry. These were made from pieces of the Roman temple that had occupied the site previously, as well as other Roman buildings, such as the Mérida amphitheatre. The double arches were an innovation, permitting higher ceilings than would otherwise be possible with relatively low columns. The double arches consist of a lower horseshoe arch and an upper semi-circular arch.