The Sensex at the Bombay Stock Exchange plunged 317 points, or 1.6 percent, to close at a three-month low of 19,015, as global markets tumbled, today. The Nifty at the National Stock Exchange declined 93 points, or 1.6 percent to 5,761.The global markets also fell, as investors fretted over a political deadlock facing Italy following general elections. So key stock indices in Japan, China, Hong Kong, South Korea and Singapore lost between 0.5 percent and 2.3 percent. The European markets also took a hit.