CHICAGO -- The nature of pitching has changed over the many decades of baseball's history. Not only have aspects of the mound been altered, but the abilities of the arms and the way staffs are constructed have also evolved over time.

That makes identifying the greatest single-season performance by a pitcher a daunting task, especially for a team like the Cubs. Chicago can trace its franchise back to 1876, when there was a pitcher's box 45 feet from home plate.

During the 19th century, a pitcher might log more than half of his team's total season innings on his own. Even as recently as the 1970s, a staff might only have nine arms. Logging 300 frames was not only normal, but expected for a Cubs legend like Fergie Jenkins.

"It's all changed," Jenkins said earlier this year. "We've got to get 250-300 innings in with 35-40 starts. I had 42 starts one year. I mean, it was just part of the game."

Given those realities, for this Top 5 list of best one-year pitching performances in Cubs history, the approach was a little different. The 145-year history of the franchise was divided into four 30-year eras, plus the 25 years from 1876-1900. We picked the best season within each era, ranked those five and then selected two runners-up for each time period.

This is hardly a complete list, and some incredible seasons are not featured. With that said, here are our picks for the best one-year pitching campaigns in Cubs history.

1) Fergie Jenkins, 1971
Era: 1961-90

Jenkins began his 1971 tour with a 10-inning, complete-game victory opposite the legendary Bob Gibson on Opening Day. From there, the greatest pitcher in Cubs history cruised to a 24-13 showing with a 2.77 ERA. He struck out 263 batters, walked 37 and completed 30 of his 39 starts (325 innings). Jenkins, who beat Tom Seaver for the National League Cy Young Award, was in the middle of a streak of six straight 20-win campaigns. His performance was worth 9.6 WAR via Fangraphs and 10.1 WAR via Baseball-Reference.

Runners-up:
Dick Ellsworth, 1963: 22-10, 2.11 ERA, 290 2/3 IP, 6.6 fWAR, 10.2 bWAR
Rick Reuschel, 1977: 20-10, 2.79 ERA, 252 IP, 6.5 fWAR, 9.5 bWAR

2) Jake Arrieta, 2015
Era: 1991-2020

Arrieta had a 7.23 ERA with the Orioles in 2013 when the Cubs landed the right-hander via trade. Looking back now, the deal was one of the great heists in Chicago history. By '15, Arrieta had blossomed into a true ace and an NL Cy Young Award winner, helping Chicago turn into a legitimate World Series contender. That summer, he went 22-6 with a 1.77 ERA (including an otherworldly 0.75 ERA in the second half) and 236 strikeouts against 48 walks in 229 innings. Arrieta then fashioned an 11-strikeout shutout of the Pirates in the NL Wild Card Game to ignite a reversal of October fortunes for the Cubs.

Runners-up:
Greg Maddux, 1992: 20-11, 2.18 ERA, 268 IP, 7.0 fWAR, 9.1 bWAR
Mark Prior, 2003: 18-6, 2.43 ERA, 211 1/3 IP, 7.8 fWAR, 7.4 bWAR

3) John Clarkson, 1885
Era: 1876-1900

What Clarkson accomplished in 1885 is almost unfathomable by today's standards. It also makes it incredibly difficult to know just where his performance should rank on a list like this one. So, with apologies to his 14.9 bWAR showing in 1887, let's put Clarkson's amazing '85 right here in the middle. He went 53-16 with a 1.85 ERA and 12.9 bWAR in 623 innings, accounting for 61 percent of Chicago's frames that year. His win total is the second-highest in baseball history. Only Old Hoss Radbourn's 1884 campaign (59 or 60 wins, depending on different sources of research) is better. Clarkson's innings total rank eighth all-time for one year. In '85, he made 70 starts for the White Stockings and 68 were complete games.

Runners-up
William Hutchison, 1891: 44-19, 2.81 ERA, 561 IP, 7.0 fWAR, 10.1 bWAR
Clark Griffith, 1898: 24-10, 1.88 ERA, 325 2/3 IP, 5.3 fWAR, 10.7 bWAR

4) Mordecai Brown, 1909
Era: 1901-30

Throw a dart at Three Finger Brown's Cubs career page and pick a season. He was that good. From 1904-10, specifically, Brown was on a spectacular run, going 160-66 with a 1.56 ERA over that span. His 1.04 ERA in '06 is a single-season club record, but his '09 performance makes this list. That year, Brown went 27-9 with a 1.31 ERA in 50 games. He started 34 games, completed 32, finished 15 and is credited with seven saves. Overall, Brown struck out 172 and walked 53 in 342 2/3 innings. That '09 showing included 7.3 fWAR and 9.5 bWAR.

Runners-up
Pete Alexander, 1920: 27-14, 1.91 ERA, 363 1/3 IP, 6.6 fWAR, 11.9 bWAR
Ed Reulbach, 1905: 18-14, 1.42 ERA, 291 2/3 IP, 4.4 fWAR, 9.1 bWAR

5) Bill Lee, 1938
Era: 1931-60

Reds catcher Ernie Lombardi took home the NL MVP Award in 1938, but it was a pitcher who finished second in the voting. That was right-hander Lee, who helped lead that '38 squad to the World Series. Lee paced the Majors with 22 wins and a 2.66 ERA while leading the NL in starts (37) and ERA+ (144). He logged 291 innings, ending with 121 strikeouts and 74 walks. His season was worth 8.0 bWAR -- the highest for this 30-year stretch in Cubs history.

Runners-up
Claude Passeau, 1940: 20-13, 2.50 ERA, 280 2/3 IP, 6.0 fWAR, 6.9 bWAR
Lon Warneke, 1933: 18-13, 2.00 ERA, 287 1/3 IP, 4.7 fWAR, 6.6 bWAR