A bull market that lasted more than a decade became a bear market in less than a month.

The coronavirus was the catalyst, but not necessarily the cause. Maybe no one could have seen a pandemic coming, but stocks had reached valuations that suggested Wall Street thought nothing could ever go wrong.

A few weeks later, the prevailing attitude seemed to be that nothing would ever be the same again. At least nothing good. The S&P 500 fell more than 35 percent from the closing high on Feb. 19 to the low on March 23. It lost 20 percent in the first quarter.

But as the second quarter got going, the mood among traders grew less gloomy as virus infections approached or passed their peaks in hot spots like New York, Italy and Spain. Stocks remained well off their highs, but well off their lows, too, after a furious recovery. The S&P rose more than 25 percent from that March 23 low to April 14.