Yes, literally. Real-life years.
The process involved, among other things, collecting roughly eighteen thousand pieces of Ancient Currency from an instanced event called Dynamis. A typical Dynamis run would drop somewhere in the neighborhood of one hundred pieces, and on rare occasions a special piece with the value of one hundred regular pieces would drop as well to bring the total to two hundred. Dynamis could only be done once every three days, so if everyone in the Dynamis group cooperated and poured all the currency into building up one person's Relic weapon, it'd still take around 150 runs just to build up the proper amount of ancient currency. 150 runs with one run every three days adds up to around a year and a half. Dynamis was not something you could run solo, either - you NEEDED those other people in order to earn your currency.
And that's speaking of an ideal situation, where everyone in the group is happy with building up one person's weapon - often it was the case that several people were trying to build weapons, and so the currency would need to be split among them. Most serious relic-builders needed to purchase some, if not most of their currency from other players in order to get their relic done in less than five years - and currency was not sold cheap. I sold around 200 currency at one point, and that was enough to purchase a Cleric's Briault for myself, at the time the best of all healer body armors and one of the more expensive crafted items in the game. Being seen with a relic usually meant that you were REALLY good at earning gil in FFXI.
And, of course, while currency was the grindiest part of the relic, it was not the only part. You also needed to present a large number of crafted items as part of the quest, many of which could only be created by top-tier crafters. You also needed to defeat specific notorious monsters in Dynamis to obtain special items needed as part of the relic process. These monsters were difficult to pop, and in the case of the monsters for the final stage could actually warp out of the fight if not defeated in a specific way (for many, that specific way was never actually puzzled out by the FFXI community; the preferred solution was to pop all cooldowns and zerg the thing fast enough so that even if it tried to warp, it'd die before the casting animation finished).
The so-called "relic grind" in this game is a complete laugh compared to the utter horror of the FFXI relic. I never would have touched the Relic grind in FFXI. In FFXIV, I'm working on two, with the Atmas stored up for two more if I ever feel the urge.
On the flip side, though, as a result of this ridiculous difficulty, there was no expectation in the FFXI community that a player should go out and obtain a relic weapon. They were powerful, yes, the strongest weapons in the game by far at the time, but no one would ever call you a bad Warrior just becuase you had no plans of obtaining a Bravura (the WAR relic). It was recognized that Relics were special, an above-and-beyond kind of thing that took a special kind of player and the cooperation of a lot of people helping that player to achieve.