In ancient, there are building that could shown the time of first season on the visible movement of sun in sky, these building are known as "chahar taghi= means four arches". in these building on first of each season, it could possible to see sun through two arches, this fascinating happening just exist in first days of each season. The picture is shown the first day of summer in chahar taghi in Shiraz, Fars, Persia.(this structure built 2000 years ago.)