Two years ago, Democratic Senators Charles Schumer and Joe Manchin sent a message to Attorney General Eric Holder and the head of the Drug Enforcement Agency: Shut down the Silk Road, they said.

Concerned by reports about a wide-open marketplace operating as a kind of stoner's Amazon, the two senators demanded action. The Silk Road kept chugging along, but the senators' June 8, 2011 letter had an immediate effect somewhere else: in the world of Bitcoin, the digital currency that helps drive the Silk Road.

Bitcoin prices promptly went over a cliff, dropping by two-thirds over the next three days. And they kept drifting downwards for months after that. The plunge seemed to confirm that the fates of the Silk Road and Bitcoin were intertwined.

Nobody really knew how big a part of the Bitcoin economy the Silk Road really played. But then the feds shuttered the Silk Road this past Wednesday, and now it's pretty clear, thanks to the Federal Bureau of Investigation's Christopher Tarbell, the special agent who signed the complaint against alleged Silk Road mastermind, Ross Ulbricht.

From February 2011 to July 2013, there were 1.2 million transactions on the site, accounting for 9.5 million bitcoins. That's about 4 percent of the 225 million bitcoin transactions that happened on Bitcoin's public block chain over the same period. The marketplace connected about 150,000 buyer accounts with just under 4,000 sellers.

That means that the Silk Road was a very big player in the Bitcoin world, but maybe not the giant that some suspected it was.

The relationship between Bitcoin and Ulbricht is clearer too, thanks to court documents that depict Ulbricht as a fan of Austrian Economic Theory and serious Bitcoin trader. According to prosecutors, Ulbricht was "Altoid,' a frequent poster to Bitcoin forums. Altoid often boasted about buying low and selling high in Bitcoin exchanges. And when Silk Road launched, bitcoin was its only method of payment.

Since that time, legitimate bitcoin use has grown, and the bitcoin economy has diversified. There's still a lot of gambling and speculation. But now you can buy groceries or electronics or cupcakes, or even pay for a cab with bitcoins

Although bitcoin took a big drop on the news of the Silk Road bust this Wednesday, it bounced back pretty quickly. So while bitcoins were down 66 percent two years ago on the mere mention of a Silk Road closure, when the F.B.I. finally came knocking, it only bashed the digital currency by about 7 percent.

That's not much worse than a typical day for bitcoin, which has moved about 2.7 percent per day, on average, since it had its big run-up this past spring, according to data compiled by Bitcoin analysis site, The Genesis Block, which has posted an interesting analysis of the relationship between bitcoin and the Silk Road.

"What you're seeing is there's a huge shift towards this legitimate economy," says Greg Schvey the Genesis Block's head of research.

In fact, the feds would probably have had a harder time investigating the Silk Road if it had been a cash-based network, says Patrick Murck, a lawyer for the Bitcoin Foundation, a non-profit group that is working to steer bitcoin into the mainstream. "It highlights some things that we've been saying all along," he says. "Bitcoin isn't this magical anonymous currency that helps people with illegal activity."