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Pantheon, a startup that maintains websites for media outlets, marketers, and other companies even when web traffic goes bonkers, has picked up $21.5 million in fresh cash.

Pantheon has cultivated a reputation as an operator of websites based on the open-source Drupal content-management system (CMS). It began supporting the popular open-source WordPress CMS a couple of months ago.

The new money will help Pantheon as it intends to maintain a larger portion of websites on the Internet. It is targeting companies looking to spend somewhere between a few hundred and several million dollars a year.

“Between those two customer [types] and use cases are a ton of websites and a ton of underserved marketing teams,” Pantheon cofounder and chief executive Zack Rosen said in an interview with VentureBeat.

Other startups that run websites for businesses have announced venture funding in recent months, signifying investors’ current interest in the market as a whole.

Squarespace raised $40 million. Weebly also took on $40 million. WordPress-focused WP Engine picked up $15 million. Earlier-stage Brandcast received $1.5 million.

And Automattic, the company behind WordPress, revealed a $1.16 billion valuation a few weeks ago when it announced a $160 million funding round.

Even with all of that competition, Rosen believes his company has plenty of potential.

“We have a goal to power around 30 percent of the web,” he said. “That is a very long-term ambition.”

Developer-friendly advantages help. For example, Pantheon can give multiple developers their own test environments containing code and content and then merge their changes. Pantheon also offers a command-line interface to let developers make changes from their desktops.

At the same time, Pantheon intends to make its cloud-based service for managing sites even easier to use, for marketers and developers alike — not unlike, say, Google Analytics, Twitter, or Salesforce’s ExactTarget.

Billboard, National Review Online, and the New Republic run sites on Pantheon, along with the Columbia Law School, Kendall-Jackson, Tableau Software, and the United Nations. In total, Pantheon maintains upwards of 65,000 sites and claims thousands of paying customers.

Pantheon, based in San Francisco, started in 2010. Around 40 people work for the company now, and that number is set to double over the next year, Rosen told VentureBeat in an email.

Scale Venture Partners led the round. OpenView Venture Partners, Baseline Ventures, First Round Capital, Floodgate Fund, and Foundry Group also participated.

The new money will help Pantheon expand its geographic footprint, improve the performance of its infrastructure, and add to its dashboard for making tweaks across many sites.

To date Pantheon has raised $28.8 million, including a $5 million round from 2012.

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