Medium, the online publishing platform led by Twitter co-founder Ev Williams, just announced that it has raised $50 million in Series C funding.

It’s been less than a year since Medium raised a $57 million Series B, but Williams wrote that the company decided to raise additional funding “to bolster our resources now given the demand we’ve seen for the vision we are building toward.”

The round was led by Spark Capital, which had also invested in Twitter. Spark’s Kevin Thau (previously an executive at Twitter) explained the investment in a post, arguing that there’s an opportunity for more “verticalized” social media experiences and contrasting “the thoughtful, timeless nature of Medium” with the ephemerality of Snapchat.

He added:

This is why we are excited about Medium. The hardest thing for companies to do is focus, but when you do it aligns everything. Medium is solely focused on being the best place to read and write interesting stuff. A single purpose publishing tool, network, and ecosystem built to share the written word.

Williams also said that Andreessen Horowitz’s Ben Horowitz and JLabs CEO Judy Estrin are joining Medium’s board of directors, while Greylock’s David Sze is stepping down. (Greylock’s Josh Elman will remain.)

Earlier this month, the company revealed that hundreds of independent publications, including The Awl and Pacific Standard, had agreed to go all-in on the Medium platform.