Stelae have long been put to commemorative and memorial purposes. The Ancient Persians, Egyptians, Greeks and Romans all erected monolithic stone blocks, from the minute to the massive, to record battles, mark graves, celebrate victories and commemorate significant events.
But nowhere has a field of stelae been created on such a colossal scale, or to such powerful effect, as at the Memorial to the Murdered Jews of Europe.
Opened on 10 May, it is dedicated to the Jewish victims of the National Socialist reign of terror.
Its location in the heart of Berlin's newly created Parliament and government district signifies a declaration of historical responsibility, underlined by the memorial's open form, which allows for personalised remembrance, commemoration and mourning.
Designed by New York architect Peter Eisenman, it comprises 2,711 gunmetal-grey reinforced concrete stelae, each uniquely positioned on a uniform grid to form a wave-like progression across an undulating site, which drops to 2.4m below street level in places. All of the stelae have an identical plan dimension of 2.38 x 0.95m, although they vary in height from a trace on the ground to 5m high, progressing from the field's boundary to the central areas. Precision-positioned to a narrow spacing of just 0.95m, the stelae create orthogonal footpaths. Visitors progress from the ground-level edge into central places, where looking up offers a mere glimpse of sky between the towering concrete forms. An overwhelming sense of disorientation is increased by the slight tilt of most stelae. Collectively, these leaning monoliths create an apparent wave across the field.
The site is in an area that was known as the 'Dead Zone' during the Cold War and had lain empty since the Second World War. It was cleared of existing foundations and its topography of craters and dips modulated to create a series of terraces on which the founding level for large groups of stelae would be constant. Within this uneven landscape each stele rests on two single reinforced concrete strips that were cast in a steel shutter over a fill-layer of sand.
Precision was necessary to create the top plane for each unique foundation, thus ensuring the exact individual stele tilt, up to a maximum inclination of 2°. Only a few stele remain upright.
Each hollow concrete stelae has four sides and a top, precast off-site. Engineer Buro Happold had to develop a construction process comparable with industrial manufacturing to achieve the huge numbers required. Trials were conducted on two-piece, five-piece and monolithic forms.
Monolithic casting in a highslump concrete mix (to DIN 1045) created an aesthetically more permanent presence that met with the approval of both Eisenman and the client.
Stelae were cast at a mass-production rate of 10 or 11 a day. A three-piece steel shuttering system enabled pours of up to 18cm for each side. A thicker top allowed the stelae to be cast upside-down, optimising concrete placement and compaction. Galvanised steel reinforcement was calculated to minimise crack widths to less than 0.1mm. Each stele was inverted to upright before the shuttering was removed and stored in a controlled workshop environment to permit optimal curing and allow surface graffiti treatment. Stelae up to 2.5m high were transported vertically, with taller monoliths laid on a flat-bed truck.
Groundworks between foundations included rainwater drainage lines, land drains and lighting cabling. Once the stelae were erected, the fine modulation of the undulating field topography was expressed by placing open-jointed concrete paving stones that allow water filtration into the sandy ground below.
Rainwater collects from the field's 12 low points into a drained water-retention tank.
Hidden below ground level at the south-east corner of this extraordinarily moving memorial is an Ort (place) of Information, a knowledge centre providing visitors with information relating to the Holocaust.
The 2,500m 2 building had to be anchored beneath the memorial to prevent uplift from the high ground-water table just 2-3m below ground level. The Ort is literally submerged in water, requiring Buro Happold to develop watertight perimeter walls in combination with injection grout beds to achieve a safe watertight excavation. In reality, the Ort is a single basement building with no superstructure above it to keep it down, a model for an increasing number of buildings being built below ground to minimise environmental impact.
Permanent restraint against the tendency of the building to float is provided by steel anchors founded at depth below the Ort - see Working Details, pages 12-13.
(Net hydrostatic buoyancy forces from ground water pressure can reach up to 50kN/m 2. )The information centre's exposed 80cm waffle and rib concrete roof slab is contoured to follow the topography of the ground above, expressing in negative form the layout of the stelae standing directly above. Roof slab ribs echo pathways, waffles reflect the position of stelae. The minimum clear headroom is 3.2m, although this rises to as much as 5m, depending on the topography of the field above.
The Ort comprises four 14m square rooms separated by a double-skin wall, 95cm thick, which aligns with the pathways in the field of stelae overhead. As well as exhibiting material, the walls enclose ventilation ductwork and structural reinforced concrete columns.
With a significance to millions of Germans and to nationals of all races, the memorial has turned an undulating 19,000m 2 site into an unforgettable place of commemoration.