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U.S. stocks closed about 1.5 percent lower or more Monday, extending Friday's post-Brexit sell-off with materials leading decliners. The Dow Jones industrial average and S&P 500 ended at their lowest since mid-March.

The major indexes came off session lows as the close neared. Traders said there were more buy orders at the close when some had expected to see selling. They also said the market was lifted by investors buying stock to cover short positions.

The Dow and S&P broke below their 200-day moving averages intraday for the first time since mid-March and held below in the close. "I think you've got some technical damage here and it's to be expected. The size of the moves in the currency markets are order-of-magnitude larger than the stock market's," said Art Hogan, chief market strategist at Wunderlich Securities. "That's a hard thing to catch up with, and the knock-on effect that it has." Read More: Brexit Wiped $2 Trillion Off Markets, Standard & Poors Says The dip follows the global carnage on Friday after Great Britain stunned its trading partners with a referendum vote to part ways with the European Union.

That move triggered a global selloff that culminated in the British pound dropping to levels not seen since 1985.

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Within minutes of the U.S. markets opening on Friday, the Dow Jones had plunged 538.21 points, or 2.99 percent, to 17,472.86. Selloffs on the S&P 500 and Nasdaq had been so fast and furious overnight on Thursday that trading had to be halted to avoid triggering limit thresholds.

As markets continue to shuffle on Monday, and investors juggle uncertainties across continents, what does this intense trading represent in real terms? Just how much money is actually involved?

At the New York Stock Exchange, “the market cap declined by $685.4 billion," estimated Anastasia Amoroso, a global market strategist at JPMorgan Chase, in a phone interview with NBC News after the closing bell on Friday. By the end of trading last week, more than $2 trillion had been wiped off the global market — the biggest loss in five years.

Read More: Brexit Redux? Petition for Second E.U. Vote Hits 3 Million Signatures

The surprise outcome of the Brexit vote left many companies reeling — and scrabbling for their own exit strategy from market turmoil that, for some, had before merely registered as a vague possibility.

As investors ditched their stocks, traditional safe havens such as oil, gold, and government bonds were predictably hot favorites.

"We've already got queues forming," Tony Dobra, executive director of Baird & Co, a London-based gold bullion merchant, told Reuters.