The Dow closed up fractionally, the S&P 500 gained just over one-tenth of a percent and the Nasdaq added just over two-tenths.

Those marginal moves come after Wall Street's main indexes closed out a strong first-half of the year on Friday, with the Nasdaq posting its biggest first-half gain in 40 years, rising nearly 32%. And money managers now are looking to gauge whether the rally continues or reverses course.

Sam Stovall is Chief Investment Strategist at CFRA Research.

"What's going on today I think essentially is a carryover of the strong first half with investors questioning, you know, 'Gee, is this really a running start into the second-half, as history tells us, or are we being set up for a big disappointment?' [FLASH] My hunch is, 'cause being a student of history, that usually if we have a strong first half you have a lot of portfolio managers who are behind the curve and if they want to either earn their bonus or keep their jobs, they've got to put the pedal to the metal. And I think that ends up pushing share prices higher."

Outsized gains for megacap stocks have led indexes, but recent signs have shown a broadening rally.

Among individual movers, Tesla continued its blistering 2023 rally on Monday with a nearly 7% jump as the electric vehicle maker said it delivered a record number of vehicles in the second quarter.

Shares of major banks gained after the companies raised dividends as they sailed through the Federal Reserve's annual health check. Wells Fargo shares rose 1.7%, Citigroup climbed 1.5%, while the S&P 500 banks index jumped 1.5%.

Markets are closed Tuesday for the July 4th holiday.