Ken Burns' series "The Roosevelts" earned PBS its biggest audience in two decades, making it the documentary maker's third most popular film after "The Civil War" and "Lewis & Clark: The Journey of the Corps of Discovery."

PBS said the seven, two-hour episodes that aired last month had an average audience of 9.2 million viewers. The most popular was the first night, on Sept. 14, which had 11.7 million viewers, according to the Nielsen company.

"It was power, it was sex, it was death, it was betrayal," PBS chief programming executive Beth Hoppe said on Thursday. "But it was also World War I and World War II and the president of the United States and his wife. It was this epic tale but it was told in a very intimate way. It was a lot like 'Downton Abbey,' but it was real.

The series gave PBS its highest weekly viewer average since 1994, when Burns' series "Baseball" aired. Although the "Lewis & Clark" documentary in 1997 had more viewers, "Baseball" was stretched across a longer period, so PBS had a larger weekly audience when the sports documentary aired.

PBS went wall-to-wall with the history of Teddy, Franklin and Eleanor Roosevelt, airing each episode twice on a given night and making them available online; full episodes were streamed more than 1.85 million times, PBS said. Streams were not included in the individual episode viewing figures.

There was evidence that many people used streaming to keep up with the series as it went along, Hoppe said. After the opening episode, the fifth night β€” FDR's first two terms and the preparations for World War II β€” had the most popular episode.

Each person who watched "The Roosevelts" saw an average of nearly four hours of the series, PBS said.

Burns is working on a shorter documentary on cancer that will air in a few months for PBS. His next big documentary series, on the Vietnam War, is scheduled to air on PBS in 2016.