Example of Our Astronomical Heritage (IMAGE) International Astronomical Union Caption This is one of the 177 Antas, a distinctive form of megalithic tomb found in the central part of the Alentejo region, Portugal, and in the provinces of Badajoz and Cáceres, in the Extremadura region, Spain. These tombs are thought to have been constructed from c. 4000 B.C. onwards. The range of orientations of the 177 monuments corresponds almost exactly to the range of possible rising positions of the sun. Credit I. Gomes (www.flickr.com/photos/ivogomes) Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.