Fifty-four companies have weathered economic busts, disruption from newer players, and methodological changes on Fortune’s end in calculating the list to appear in every Fortune 500 since 1955.

In this year’s list, these companies accounted for nearly $2.1 trillion in revenue, or 16% of the Fortune 500’s $12.8 trillion in revenue—surviving and even thriving by selling products needed regardless of era. That includes food and beverage sold by firms such as Pepsi and Kellogg, or aerospace and defense firms such as Boeing.

Other firms with extreme longevity may seem less obvious. Consider Motorola Solutions, a spin-off of a company known for making cellphones. Such a product would have been bizarrely out of place in 1955. Though explaining the company’s endurance on the list doesn’t require time travel. Like some other companies that have made it all 64 years on the Fortune 500, Motorola Solutions’ predecessor has gone through spin-offs and rebrandings. Once upon a time, the company was part of a firm known as Galvin Manufacturing Corporation, a car-radio maker founded in 1928.

And while companies have come and gone on the Fortune 500 through its 60-plus years, the largest of the large have continued to endure. Since 1955, just three companies have taken No. 1 on the Fortune 500: Carmaker General Motors, oil and gas giant Exxon Mobil, and finally, today’s king, Walmart.

Even today, all three firms remain in the top three even as they face impending threats. GM and Exxon for instance both face the rise of electric cars from companies such as Tesla. Walmart, which upended GM and Exxon with its revolutionary one-stop shop of cheap goods for the first time in 2002, is now facing a coup from e-commerce titan Amazon.

Tesla gained about 123 spots on the Fortune 500 this year, now resting at 260. Amazon on the other hand has been steadily climbing the ranks, breaching top 10 for the first time on the back of 2017’s revenue. But the steady shuffle of these three giants suggests that despite tech’s ever-growing presence—toppling the king of the list will not be as easy as it seems.

So, could tech firms one day become No. 1 on the Fortune 500? Investors certainly seem to think there’s a good chance. While Walmart is the largest firm by revenue, investors deem iPhone maker Apple a far more valuable company, worth above $900 billion versus Walmart’s $241.6 billion. Amazon, a more direct comparison with the brick-and-mortar retailer, is valued at $763.8 billion.