A possible suggestion for the gimlet was the succession of inclined planes by which one mounted to the top of an Assyrian or Chaldean palace; these planes rising gradually on each of the four sides, so as to form together what might be called a square spiral. It is possible that a circular spiral may have been traced later around some cylindrical shaft or column, and given the first suggestion for the screw or gimlet. Of course, a gimlet is a kind of screw. The Greeks do not seem to have applied their inventiveness after the time of Dædalus to mechanical appliances, but to works of art and systems of religion and philosophy. One of their most important inventions may be said to be mid-way between: it consisted in adding vowels to the Phoenician alphabet and producing the basis of the Latin and succeeding alphabets. The Greeks were not naturally of a warlike disposition, and their peculiarly jealous temperament prevented the various states and cities from combining and forming a great nation. Their energetic character and great intellectuality saved them, however, when Darius, King of Persia, invaded Greece in 490 B. C. By that time the Greeks had raised and trained an army of great excellence. No especial inventiveness seems to have been exercised, but the equipments of the men, their organization, their armor, their weapons and their discipline had been brought to a standard exceedingly high. All these advantages were needed; for the Persians were a warlike people, their King Darius was an ambitious and successful conqueror, and the number of Persians that invaded Greece was far greater than the number that Greece could raise to fight them. Had the Greeks been destitute of invention they would have followed the most obvious course, that of shutting themselves up inside the protection of the walls of Athens. Had they done this, the Persians would have surrounded the city, shut them off from supplies from outside, and slowly but surely forced them to surrender.