The stock market hit a new milestone Monday.
"What these central banks are basically saying is, 'We are going to keep these rates down so go buy stocks,'" said Patrick J. O'Hare, chief market analyst with Briefing.com.
The bellwether index reached a high of 2,001.95 on Monday before falling below the 2,000 milestone. The index was up 9.74 points, or 0.49%, to 1,998.14 in afternoon trading.
Stocks also rose on merger and acquisition news.
On Sunday, Swiss pharmaceutical giant Roche said it has agreed to acquire Northern California biotech firm InterMune in an $8.3-billion deal.
Shares of InterMune climbed $19.10, or 35.50%, to $72.90 on Monday.
Also on Sunday, fast-food giant Burger King, based in Miami, and Canadian coffee-and-doughnut chain Tim Hortons said that merger discussions were underway and that a "new publicly-listed company would be headquartered in Canada, the largest market of the combined company."
Burger King shares rose 19.25%, $5.22, to $32.33.
The S&P 500 is up 9% since the start of the year.