Photo taken on April 30, 2016 shows the old walls of the Nuraghi of Barumini in Sardinia, Italy. Nuraghi, which date back to the late 2nd millennium B.C. in the Bronze Age, is the main type of megalithic edifice found only in Sardinia. The use of these beehive-like buildings remains unknown. Main assumptions are religious temples, meeting halls or military strongholds. As the finest and most complete example of this form of prehistoric architecture, the Nuraghi of Barumini were declared World Heritage by UNESCO in 1997. (Xinhua/Jin Yu)

Photo taken on April 30, 2016 shows the old walls of the Nuraghi of Barumini in Sardinia, Italy. Nuraghi, which date back to the late 2nd millennium B.C. in the Bronze Age, is the main type of megalithic edifice found only in Sardinia. The use of these beehive-like buildings remains unknown. Main assumptions are religious temples, meeting halls or military strongholds. As the finest and most complete example of this form of prehistoric architecture, the Nuraghi of Barumini were declared World Heritage by UNESCO in 1997. (Xinhua/Jin Yu)

Photo taken on April 30, 2016 shows the main court and a well of the Nuraghi of Barumini in Sardinia, Italy. Nuraghi, which date back to the late 2nd millennium B.C. in the Bronze Age, is the main type of megalithic edifice found only in Sardinia. The use of these beehive-like buildings remains unknown. Main assumptions are religious temples, meeting halls or military strongholds. As the finest and most complete example of this form of prehistoric architecture, the Nuraghi of Barumini were declared World Heritage by UNESCO in 1997. (Xinhua/Jin Yu)

Photo taken on April 30, 2016 shows an old tower of the Nuraghi of Barumini in Sardinia, Italy. Nuraghi, which date back to the late 2nd millennium B.C. in the Bronze Age, is the main type of megalithic edifice found only in Sardinia. The use of these beehive-like buildings remains unknown. Main assumptions are religious temples, meeting halls or military strongholds. As the finest and most complete example of this form of prehistoric architecture, the Nuraghi of Barumini were declared World Heritage by UNESCO in 1997. (Xinhua/Jin Yu)

Photo taken on April 30, 2016 shows an old tower of the Nuraghi of Barumini in Sardinia, Italy. Nuraghi, which date back to the late 2nd millennium B.C. in the Bronze Age, is the main type of megalithic edifice found only in Sardinia. The use of these beehive-like buildings remains unknown. Main assumptions are religious temples, meeting halls or military strongholds. As the finest and most complete example of this form of prehistoric architecture, the Nuraghi of Barumini were declared World Heritage by UNESCO in 1997. (Xinhua/Jin Yu)

Photo taken on April 30, 2016 shows the main court of the Nuraghi of Barumini in Sardinia, Italy. Nuraghi, which date back to the late 2nd millennium B.C. in the Bronze Age, is the main type of megalithic edifice found only in Sardinia. The use of these beehive-like buildings remains unknown. Main assumptions are religious temples, meeting halls or military strongholds. As the finest and most complete example of this form of prehistoric architecture, the Nuraghi of Barumini were declared World Heritage by UNESCO in 1997. (Xinhua/Jin Yu)

People visit the Nuraghi of Barumini in Sardinia, Italy, April 30, 2016. Nuraghi, which date back to the late 2nd millennium B.C. in the Bronze Age, is the main type of megalithic edifice found only in Sardinia. The use of these beehive-like buildings remains unknown. Main assumptions are religious temples, meeting halls or military strongholds. As the finest and most complete example of this form of prehistoric architecture, the Nuraghi of Barumini were declared World Heritage by UNESCO in 1997. (Xinhua/Jin Yu)

Photo taken on April 30, 2016 shows original stairs of the Nuraghi of Barumini in Sardinia, Italy. Nuraghi, which date back to the late 2nd millennium B.C. in the Bronze Age, is the main type of megalithic edifice found only in Sardinia. The use of these beehive-like buildings remains unknown. Main assumptions are religious temples, meeting halls or military strongholds. As the finest and most complete example of this form of prehistoric architecture, the Nuraghi of Barumini were declared World Heritage by UNESCO in 1997. (Xinhua/Jin Yu)

Photo taken on April 30, 2016 shows old walls and the central building of the Nuraghi of Barumini in Sardinia, Italy. Nuraghi, which date back to the late 2nd millennium B.C. in the Bronze Age, is the main type of megalithic edifice found only in Sardinia. The use of these beehive-like buildings remains unknown. Main assumptions are religious temples, meeting halls or military strongholds. As the finest and most complete example of this form of prehistoric architecture, the Nuraghi of Barumini were declared World Heritage by UNESCO in 1997. (Xinhua/Jin Yu)