Stocks closed higher on Monday, with merger activity driving the Dow and S&P to fresh two-and-a-half-year highs, the latest in a series of mileposts that point to more gains ahead.

Buying accelerated after the S&P 500 broke through the 1,313 mark, taking it further into levels that prevailed before the financial crisis. Two stocks rose for every one that fell on the New York Stock Exchange, even though the day's rise was on lighter-than-average volume.

Diversified industrial company Danaher Corp agreed to buy medical diagnostics company Beckman Coulter Inc for about $6.8 billion. Oil driller EnsCo Plc said it would buy Pride International Inc

for about $7.3 billion.

Based on the latest available data, the Dow Jones industrial average <.DJI> was up 69.25 points, or 0.57 percent, at 12,161.40. The Standard & Poor's 500 Index <.SPX> was up 8.14 points, or 0.62 percent, at 1,319.01. The Nasdaq Composite Index <.IXIC> was up 14.69 points, or 0.53 percent, at 2,783.99.

(Reporting by Caroline Valetkevitch; Editing by Andrew Hay)