Amazon, the seemingly unstoppable internet retail giant, marked another milestone Tuesday when the price of one share of its stock on broke $1000.

That price put Amazon's present market value around $478 billion, double that of the world's biggest brick-and-mortar retailer Walmart, and more than 15 times the size of competing big-box store Target. The price of the company's shares has risen 40% this year.

In 2015, Amazon surpassed Walmart as the most valuable retailer in the United States by market capitalization, and was in the third quarter of 2016 and the first quarter of 2017, the fourth most valuable public company in the world.

Choosing to avoid stock price splits that make stocks more affordable to prospective buyers on the market, Amazon has focused on returning value to the shareholder through relentless innovation, market dominance and expansion past their focus internet retail. Beginning as a website for buying books on the nascent marketplace of the Internet of the mid-90s, no one expected Amazon to explode and tranform the idea of e-commerce.

Since their 1997 introduction to public trading, the Seattle-based company has changed the way internet shopping works, made their own tablets and media streaming service, and even launched their own movie studio that produces and distributes Academy Award-winning films like Manchester By The Sea.

Only four other U.S.-listed companies currently have shares priced at similar levels: internet travel booking network Priceline, homebuilder NVR Inc., food producer and maritime transportation company Seaboard Corp., and Warren Buffett's Omaha-based holding company Berkshire Hathaway Inc.

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