The four biggest tech companies finished the day each worth more than $ 1 trillion, a landmark that was last reached before the Covid-19 pandemic struck the U.S. 

The landmark shows the resilience of the tech industry in the face of a global pandemic, recession and record unemployment. 

Alphabet was the latest to re-enter the trillion-dollar club, reaching $ 1.02 trillion in market value at the close of trading. Apple was valued at $ 1.64 trillion, followed by Microsoft at $ 1.61 trillion. Amazon, which has largely benefited from stay-at-home orders that battered most companies, was valued at $ 1.52 trillion as of market close. 

The valuations were boosted by a strong day for U.S. markets. The Dow Jones Industrial Average rose 459 points, or 1.78%, while the S&P 500 finished up 1.59%. The tech-heavy Nasdaq Composite jumped 2.21% to an all-time high.

The technology giants first reached the milestone in late January and held onto gains into February, before the pandemic caused markets to plummet.