You've heard people say, "Rome wasn't built in a day," usually right after explaining their third failed attempt to get investors for their "unique" new fashion company. But, while that saying is too often used to justify people's choices, there is a reason why it is so well known - it's true.

Car companies and the models they design and build take years to layout, fund, and test, which is why so many of our favorite cars have changed significantly since they first appeared in the magazines of yesteryear.

Porsche, for example, conceived the 911, a current world-beater in performance, experience, and name cache. But the modern 911 models we see on the road now are not the same as they once were.

The 911 has been slowly pushed down a Porsche-laid path towards the reality of a perfect sports car, and today, we look at the stones that built that path.

Dating back to the '60s, these are a handful of the 911 models that, while no longer being produced, allowed its name to continue through 58 years of progress.

Porsche 911 L

Porshce 911 L
Via BringATrailer

For Porsche, the 911 was an instant hit, meaning they had to shift new versions around to suit as many customers as possible. Some wanted comfort and an open-top, some wanted performance, and some wanted a standard 911 experience. This middle-of-the-road 911 came in 1968 as the 911 L.

The L came into existence only because Porsche decided to introduce a new entry-level 911, the 911 T. The T would have less power (110hp) and a 4-speed transmission. The engine and basic structure from the existing base model would go into the new 911 L, which was now one step up from the new base model 911 T. Porsche recently brought back the 911 T in its classically simple form.

As a one-year-only model, the 911 L is increasingly rare these days and collectors spend top dollar for numbers-matching examples. The L came from the factory with a 130hp 2.0-liter flat-six engine that could be paired to either a 5-speed manual or 4-speed Sportomatic transmission.

Related: This Is Why Porsche 911s Hold Their Value So Well

Porsche 911 E

Porsche 911E
Via BringATrailer

The evolution continues with the 911 E. This particular model entered production just one year after the 1968-only 911 L with the intent to replace it.

The reason being that Porsche had just designed a fresh generation of flat-sixes that needed a home. These new and bigger, 2.2-liter flat-sixes made anywhere from 140 hp to 165 hp, depending on trim level. The 911 L, with its 2.0-liter 13 0hp engine, was replaced in favor of the new 911 E that sported the fancy new engine.

Also, a quick note of perspective to remember is that the NB Miata made 140 hp in 1998, exactly 30 years after the 911 L did it.

Porsche 911 R (Kind Of)

Porsche 911R
Via ClassicDriver

The mid-60s was a time of enthusiasm for Porsche, not in production cars, though - in racing. The desire for a super 911 was rooted in the minds of several Porsche engineers but none more than Ferdinand Piëch, Ferry Porsche's nephew, who was now the head of R&D in Zuffenhausen.

In 1966, Piëch started by taking a 911 S and stripping it of all road-going dignity. The metal body panels were replaced with fiberglass, the windows were taken out and replaced with plexiglass, and everything but essentials were ripped out of the interior. Every little detail was combed through with Piëch's mantra of lightweight in mind.

The 911 R was given a 210 hp flat-six seen through a factory-installed 10,000 rpm tachometer. There are no confirmed stories of the engine reaching that insane redline, but we would sure love to hear it.

The now-1760 lbs prototype was dubbed the 911 R, with the "R" standing for Racing. But the 911 R didn't do much racing at all. The GT racing class required 500 road-legal examples to be sold to meet homologation requirements, and the Porsche accountants swore the R could never find its way into 500 civilian driveways.

As a result, the four prototypes, along with only 20 additional units, were produced in total, making it one of the rarest Porsches to ever go on sale. You'll notice we said "kind of" in the subheader, and that's because Porsche produced an additional 991 examples for the 991-generation 911 in 2016.

Related: What We Know About The Porsche 911 R

Porsche 911 Carrera RS 2.7

Porsche 911 Carrera RS 2.7
Via Porsche

As Porsche continued to expand its racing prowess throughout the early 1970s, they would once again attempt to build a dominant GT-class racecar. And finally, they succeeded with the 911 Carrera RS 2.7.

In 1972, Porsche had its heart set on the GT-class races of the following season and went to work once again. The Carrera RS 2.7 debuted that same year with a 210 hp 2.7-liter flat-six and a 911 R-inspired lightweight motto.

The RS was a showstopper. The iconic ducktail spoiler was the first wing to ever be fitted on a production 911, and its wide wheel arches gave it a classic racecar stance as well as some extra room for rubber.

The initial 500 unit-production run soon had to be doubled after demand increased and then tripled to fulfill even more orders. A total of 1,580 were built, 200 of which were ordered with the "lightweight" package, a trim that weighed just 2,150 lbs.

The actual race version was dubbed the 911 RSR 2.8, an FIA Group 4 racecar that began Porsche's dominance in GT-class racing. The RSR, in its first season, won the 24 Hours Of Daytona, 12 Hours of Sebring, and the Targa Florio, earning the RSR the ISMA Drivers Championship as well as the World Manufacturers Championship.

Porsche 911 SC

Porshe 911SC
Via BringATrailer

We now find ourselves in the year 1978 and Porsche. By now, Porsche had decided to downsize the 911 family from four models to two. In 1977, you could buy a base 911, the 911 Carrera, 911 S, or 911 Turbo. In 1978, a new model called the 911 SC would take the Carrera and base model and combine it into one model.

The SC stood for "Super Carrera," a badge that would result in a new 3.0-liter engine making 180 hp in its initial 1978 model year. Power was increased over its 5-year-long production run and peaked at 204 hp in 1983 when it was then re-replaced by the 911 Carrera.

The SC continues to be a favorite of classic 911 collectors as it inherited the wider body of the 911 S and was given nearly 30 more horsepower by the end of its run.