These are the graph paper sketches that became 'Super Mario Bros.'

Looking at the technological wonders emerging from this year's Electronic Entertainment Expo, it's hard to imagine that, not very long ago, developers created video games with tools as rudimentary as a pencil and paper.

But that's exactly what happened in Japan, where the original "Super Mario Bros." was designed entirely by hand.

During Nintendo's E3 press conference, game designers Shigeru Miyamoto and Takashi Tezuka described the humble leg work that went into creating the original "Super Mario Bros." In a video, they showed off some of the hand-drawn sketches that ultimately became the iconic side-scrolling adventure.

"Back in the day, we had to create everything by hand," Tezuka explained via a translator. "To design courses, we would actually draw them one at a time on these sheets of graph paper. We'd then hand our drawings to the programmers, who would code them into a build."

While they were looking through their original design documents to help develop Super Mario Maker, they stumbled across some of their first drawings.

"It's very precious," said Tezuka, holding up one of the sheets.

The video was part of the hype for the newly announced Super Mario Maker, which will give gamers the chance to do what Tezuka and Miyamoto did 30 years ago: Design their own levels for Mario and his pals to explore.

But unlike in the early 1980s, fans will be able to do it without a pencil and paper. In fact, the game is based on the actual tool Miyamoto and Tezuka used to create later installments of "Super Mario Bros."

"The more we worked with it, the more we realized we could also turn it into something everyone could enjoy," Miyamoto said.

The game comes out in September. Watch the video (via Kotaku):