Research on a 6000 year old prehistoric artifact indicated that the enigmatic prehistoric megalithic temples of the Maltese Islands to which the artifact was closely related, were not just cult temples, but were primarily solar year calendars, versatile and accurate to an unbelievable degree, especially when considering their age. However the research also indicated that anomalies, the results of past geological events known only from legends, had completely obfuscated clear evidence of their primary purpose; had obfuscated evidence of how they were designed, and how they functioned. The book begins with a brief description of the prehistoric culture that built the megalithic calendars; an agrarian culture based on the cultivation of the cereals. Then it looks closely at the various aspects of these megalithic structures that gave hint to the temple/calendar design and how it functioned. How they evolved from the earliest concepts to the later improved designs. It shows how the early design was tested for functionality, and the surprising results that were obtained from the tests that prove beyond doubt such an intentional design. Then it looks into the sources of the anomalies that had become evident. The book here takes a closer look at the main anomalies, and the evidence of their origins. How the Australian astronomer George F Dodwell from the early astronomical research from 3000 years ago, discovered the origin of the anomalies. How recent research of the last decades led to discovering a possible cause of such anomalies. What cataclysmic effect the source of the anomalies had on the Earth and humanity, leading to sudden and severe climate change and great upheaval in civilisations in most parts of the old world. Plus a glance at the various other sources of corroborating evidence. Next the book takes another closer look at how these anomalies are evident in the various calendar structures, in the sequential changes in their design and the way it evolved, and in the changes in their orientation. Based on these findings, one later and very curious calendar design type was reverse-engineered. This resulted in discovering a practical and accurate method that shows how reading the date from the later structures was possibly done. It includes the possibility of the accurate forecasting of the equinox and solstice days, an efficacious method that is equal or better than any that were and are used today. Thus providing further proof of their real intended function and how the megalithic calendar design evolved. The book ends by taking a look at the Megalithic temples of Malta within the context of the ancient legends. The calendars are evidence that prove that the ancient legends and myths of great cataclysms are based on historical fact. That they are not just ancient fiction created for amusement, but the result of events of grave concern; of grave concern not only to the ancients but also to present and future generations.