This book contains the "relics" that were saved from the lost treatises of Euclid , as well as the relevant testimonies of the ancient authors. The book specifically refers to the 5 lost mathematical works of Euclid with titles: "Pseudaria" , "On divisions" , "Conic elements" , "Places on surfaces" and "Conclusions " . It still contains all the information about his two works in theoretical mechanics, with probable titles "On heavy and light bodies" and "On equilibria" .