The Palace of Knossos bears unique testimony to the Minoan civilization, which was arguably considered as the first centrally organized civilization to flourish in Europe and amongst the first civilizations worldwide. It is also unique because of its continuous habitation from the Neolithic to the Mycenaean Age, while the city of Knossos continued to be an important city-state down to the Hellenistic era, the period of the Roman Empire and the early Byzantine period.

The Palace of Knossos, the largest of the Cretan palaces, (it covers an area of 22000 sqm) and the city that arose around it are built on the top and slopes of the low hill of Kefala, where the River Kairatos meets the small Vlychia stream. Security, fertile land, water and proximity to the sea were the main reasons not only for the choice of the site as a place of habitation from earliest prehistoric times, but also for its subsequent prosperity and growth.

The first palace was built circa 1900 BC, following the leveling and landscaping of the hill. It was destroyed around 1700 BC and the new palace was erected in its place. The new palace was constructed according to a specific architectural plan, similar to that of the other palaces, befitting its character and function as the centre of political, economic and religious authority. The main feature remained the Central Court, with monumental buildings rising around it, oriented N-S.


There were entrances on every side, the most official being the Southwest and the North Entrance. The West Wing contained shrines, official halls and extensive storage areas, while the East Wing housed the royal apartments. There were also workshops, storerooms and other areas serving a variety of functions to north and south. They feature typical architectural elements of the period, such as polythyra (sets of rooms with multiple pier-and-door partitions on two or three sides) and lustral basins (small, rectangular, semi-underground rooms accessed by a small, L-shaped set of stairs). Poros-stone ashlars were used in the masonry. The floors were paved with slabs of green schist pointed with red plaster. The columns, beams and doorframes were made of wood. Gypsum slabs covered the walls (in the form of marble revetment) and floors, giving the spaces an air of luxury. Gypsum was also used for the bases of columns and jambs, seats, stairs, etc. The decoration of the rooms was supplemented by colourful plaster and frescoes.

The Palace of Knossos was the only palace to remain in use after the destruction of 1450 BC, when the Mycenaeans settled Crete. Following the final destruction of 1380 BC, large parts of the Palace were reoccupied and remodeled, mainly as private houses.

The first excavations at Knossos were carried out in 1878 by a merchant and antiquarian from Heraklion, Minos Kalokairinos, who discovered part of the West Wing of the Palace.

Systematic excavations began in March 1900 under Arthur Evans, then Curator of the Ashmolean Museum in Oxford. Two years later, the excavation of the Palace was almost complete. The fragile building materials proved extremely sensitive to weathering. During the first phase of their restoration efforts, in 1905, Evans and his colleagues restricted themselves to protecting the ruins. After 1925, however, Evans attempted a radical reconstruction of the monument, with large-scale use of reinforced concrete. Upper storeys and architectural elements were reconstructed. The timber frames and wooden Minoan columns were made of concrete, painted. The frescoes were restored and copies placed in different parts of the Palace.

Today, Evans’s reconstruction of the Palace forms an integral part of the monument and its history.

After the Second World War, extensive restoration work was carried out on the Palace by the Directors of the Heraklion Archaeological Museum N. Platon and S. Alexiou. This work was limited to the conservation of the ancient masonry, the restoration of the floors and the protection of certain areas with roofing.

During the nineties the Ministry of Culture, recognizing the problems that the monument was facing, took measures for its preservation and restoration. Under the authority of the Ephorate of Antiquities a great part of the concrete slabs of Evans’ restoration of the Palace was conserved, and paths for the visitors were developed, which reduced the wear of the monument and gave the visitors a more complete view of it.

In 2000 – 2008 a conservation project of the Palace was included in the 3rd C.S.F (Community Structural Funds). For its protection and restoration a NSRF (National Strategic Reference Framework) Project begun in 2010 and finished 2015, concerning the restoration and conservation of the monument. Indeed, a complete programme of conservation and promotion of the site was launched: conservation of masonry, gypsum stones and limestones, ancient coatings and plaster, copies of frescoes, columns and wood imitations, conservation of the Minoan pithoi, and replacement of Evans’s lightly-arched roofs.




Gypsum is one of the main building materials on the archaeological site of Knossos and was used extensively for walls, floors, column and pillar bases, door jamb sockets, stairs, etc, originating from the local quarry at the nearby hill of Gypsades.

Mineral gypsum shows a great diversity in crystal morphology and occurs in varieties with quite different macroscopic characteristics. In the Palace of Knossos the dominant types of mineral gypsum belong to the medium to coarse crystal varieties, namely “Selenite”. The identification and characterization of gypsum varieties can be intricate due to surface alterations caused by natural weathering processes or forced dehydration. The result of the aforementioned decay processes is the loss of original material mainly due to dissolution as well as the degradation of the aesthetic values that eventually leads to misinterpretation.

Within the concept of the HERACLES project, the contribution of the Crystal Engineering, Growth & Design Laboratory of the Department of Chemistry, University of Crete, focuses on two distinct but interdependent problems. The qualitative and quantitative study of the dissolution rate of mineral gypsum (a chemical process), in correlation with the environmental parameters of the area of Knossos and Heraklion, in general. In parallel, a second focus point will be on the design and evaluation of materials and multifunctional chemical compounds that will aid the restoration of the original ancient material in terms of restoring – consolidating the structural integrity of the stone constituents (i.e. crystal aggregates).


Determination of the degradation state of the Palace of Knossos

Generally, the Palace of Knossos had suffered extensive damage due to mechanical and biological factors, combined with the local microclimate and the structure of the walls. The direct exposure to sunlight, rain, wind and atmospheric pollution, the relative humidity and temperature, which ranges beyond recommended limits, and the extensive use of reinforced concrete for its restoration are the main reasons for its damage.

Indeed, the deterioration of the palace is due to the physicochemical properties of the materials, suffering the parallel effects of environmental and man-made factors.

Water (in all types, such as rain, humidity, frost) is a main factor for decay of all the materials of Knossos palace. Fluctuations in temperature precipitate the formation and deposition of salt crusts on the surfaces of the monument. The presence of soluble salts is in partly due to the prevailing sea wind that comes from the north. During periods of humidity microbial growth develops on stone and masonry surfaces.

Restoration works that took place after the palace’s discovery by A. Evans hindered its maintenance for many years. The cement additions to the architectural structures created mechanical stress and were another source of soluble salts.

The identification and analysis of major risks regarding structures and artworks’ preservation (e.g. the excessive deformation in reinforced concrete elements), the contribution to identification and analysis of materials degradation state (e.g. degradation status and corrosion of reinforced concrete elements) and proposals of restoration strategies for structures and materials will be useful for the monument.

Finally, the large number of visitors, combined with the free access previously given (until ’90’s), increased the deterioration of the palace’s vulnerable materials.

Proposed methodologies for analysis, diagnostics and conservation

IESL-FORTH has a solid experience on laser methodologies for analysis, diagnostics and conservation (cleaning) on CH monuments and objects, with emphasis to portable instrumentation and in-situ application methodologies. In this respect the contribution of the photonics for Cultural Heritage group IESL-FORTH to the works of HERACLES project focused on the Knossos archaeological site is expected to lie along the following lines:

  • In-situ diagnosis, monitoring and interventions. Portable instrumentation based on optical and laser spectroscopic analysis (LIBS, Raman, multispectral imaging etc.) will provide fast, reliable and in-situ analysis and monitoring of the weathering state and its progress on areas of interest. Among the issues that will be studied are the nature and expansion/propagation of efflorescence salts on the ancient and restored masonry as well as on the restored roofs of the archaeological site of Knossos and the preservation state of the Minoan pithoi and Evans’s fresco replicas etc. Furthermore, selected untreated and recently restored surfaces will be monitored in order to visualize the irresponse to the environmental conditions and thus assess their resistance to climate changes and evaluate the effectiveness of the treatments and /or the criticality and necessity of new restoration interventions, etc. 
  • In parallel (ex-situ) analyses based on laser spectroscopy will be carried out in the laboratory in order to characterize the structural, chemical and physical properties of the materials (ancient, new, as well as alteration forms). Moreover, novel imaging techniques as for example non-linear microscopy and 4-D surface /volume topography will be employed to non-destructively characterize, delineate and map materials aiming at gathering complementary high-resolution information for their composition and morphology


Installation of meteorological stations in the archaeological site of Knossos

Monitoring the local climatology in the vicinity of the Knossos Palace, will help the HERACLES research program, participants to access the major adverse-effects-factors that are related with the current and future change in climatic conditions. For the needs of HERACLES, it was decided to install a meteorological station to measure wind speed and direction, temperature, humidity, solar radiation and UV index. The meteorological station will be installed at the maintenance area north of the Palace, by the Coastal Research Laboratory (CRL), Institute of Applied and Computational mathematics (IACM) of FORTH.

General Remarks: The Meteorological Station will be installed on 3 meters metal mast, which should be protected from lightning strike and be able to withstand wind speeds in the range of over 8 Beaufort. The sitting position was chosen, in order to minimize the intervention at the historic environment of Knossos.

Met. Station Sitting position: The weather station will be located within the premises of the maintenance area, North of the archaeological site and outside visit area. In coperation with the Ephorate of Antiquities of Heraklion the maintenance area was chosen as the final location. The installation position is by the main gate of the maintenance area.

Lightning Protection: The mast will be equipped on its highest point with a Franklin type lightning rod. This will be grounded with a copper rod and the connection will be made with a 50mm2 copper wire.

Bioclimatology in the city of Heraklion

The following tables depict a long-term analysis of the seasonal, statistical climatic characteristics for the city of Heraklion, focusing on temperature, wind speed and rainfall on monthly basis



Linear regression of the long term data shows a statistically significant positive trend but only from 1976 until the end of the period considered (b = 0.02 °C/year, p < 0.05); the temperature increases by 0.54°Cthe last 27 years (1976-2014). Regarding the wind speed, a statistically significant upward trend, is presented for Heraklion for the entire period (b = 0.050 kt/year, p < 0.05). More specifically, during the 48 years of the considered period, the wind speed display an increase of 2.4 kt.