 The latter symbol further evolved into , then , and eventually changed to under the influence of the Latin word "mille" "thousand".According to Paul Kayser, the basic numerical symbols were , , and (or ) and the intermediate ones were derived by taking half of those (half an is , half a is and half a is ).Lower case, minuscule, letters were developed in the Middle Ages, well after the demise of the Western Roman Empire, and since that time lower-case versions of Roman numbers have also been commonly used