The ancient Beanbean Kingdom
The Beanbean Kingdom is a kingdom that features in Mario & Luigi: Superstar Saga and its remake for the 3DS, being located directly south of the Mushroom Kingdom. In the game, several hints are given as to the ancient past of this kingdom through the mentions of ancient civilizations, which I want to document in this post.
The Hoohoo Civilization
One of the first areas Mario and Luigi visit in the Beanbean Kingdom is Hoohoo Mountain in the kingdom's northwest. Among the waterfalls of this mountain sits Hoohoo Village. One of the people that live there says the following:
"Long ago, on this very mountain, the Hoohooligans developed the great Hoohoo civilization. At the summit, there still remain many mysterious remnants of this once great people."
And another one says:
"We are said to be the descendants of the people who developed the Hoohoo civilization. This land is largely populated by the Beanish peoples, but there are other races, like ours!"
It seems in the past that these Hoohooligans inhabited the entirety of Hoohoo Mountain, but their descendants confined to their village in the present. When one goes up the mountain, they indeed come across many remnants of their culture. The most notable are their Hooroglyphs, ancient letters that spell out the jokes of the civilization.
Another is the weapon Hoohooros, who functions as a boss and guards the path to the mountain summit. He is also surrounded by Hooroglyphs and can use them to fire lasers.
Lastly, there are also fiery statues on the mountain that are not explicitly tied to the civilization, but may have been made by it as they look like the people of Hoohoo Village. When doused, other statues are activated that generate small tornadoes and so may also have been made by this civilization.
Soybean Civilization
The second civilization is given less to work with. They are mentioned by an elderly resident of Beanbean Castle Town, who describes them as an advanced bean civilization from an age of flying spin-beans, tunneling mole-beans, and fast-moving dash-beans. They also had hidden treasures called Beanstones, which are jewels that can be found in modern-day Beanbean Castle Town.
The other mention of the Soybeans comes from a Toad in Little Fungitown, who says the lift that leads into the town (which is located atop tall mushrooms) was made by them:
"They say that lift was made long ago by the people of the ancient Soybean Civilization."
Given that this lift bears a crest of the Mushroom Kingdom that is shown in the Mushroom Castle and the Mushroom Kingdom embassy in Little Fungitown, it is possible that the ancient Mushroom Kingdom and the Soybean civilization used to have contact. Generally, it seems probable that the Soybeans are the predecessors of the modern Beanish people, given they inhabit the same general area.
Guffawha Ruins
At the foot of Hoohoo Mountain but outside the fields around Beanbean Castle, there sits an ancient structure called the Guffawha Ruins. Underground ruins of similar structure also extend in the western portion of Teehee Valley, a desert that sits east of the ruins in general. The Guffawha Ruins seem to have architectural elements of both the Hoohoo civilization and the Soybeans. For the Hoohoo civilization, Hooroglyphs can be found in and outside the ruins. There are also statues inside that bear resemblance to cave entrances near Hoohoo Village.
As for the Soybeans, presuming they are the ancestors of the modern Beanish, we do find some structures that resemble those of the modern Beanish in the Guffawha Ruins. The Beanish have the tendency to mark their presence with the use of smiling faces which can be seen on the rocks and door frames of the Guffawha Ruins. Furthermore, a large smiley face also adorns the outside of the ruins on the map and several statues in front of its entrance.
Given both architectural styles are present and the ruins are found on the border of Hoohoo Mountain and modern-day Beanish territories, it is likely the Guffawha Ruins were a joint effort by both ancient civilizations. It is unclear what the purpose of these ruins was, though in the present day they are the only place where Crabbie Grass, the cure for Bean Fever, grows.
Oho Civilization
The final civilization is only mentioned once and a tad indirectly. On the Oho Oasis island in the Oho Ocean in the east of Beanbean Kingdom, there are several recordings left behind by an expedition team. They were there to research to so-called Oho Civilization:
"It has been a week since our Oho Civilization Research Expedition reached this island."
On the island, two ruins of palaces can be found dedicated to the entities Firebrand and Thunderhand. During Superstar Saga, they bestow the Firebrand and Thunderhand abilities to Mario and Luigi respectively. These palaces were likely built by the Oho Civilization and were last visited 3000 years ago according to Firebrand, giving a general time frame for how long ago the Oho Civilization existed.
In and near these palaces there are also statues present. What is interesting is that smaller versions of those statues can be found underwater in the Oho Ocean and on Gwarhar Lagoon in the far southeast of the Beanbean Kingdom. This indicates the Oho Civilization spanned the entire Oho Ocean at one point and perhaps that they were an aquatic people, given sea levels were higher in the past (as Teehee Valley used to be an ocean).
Conclusion
The ancient Beanbean Kingdom was home to three separate civilization, which date back at least 3000 years ago. Whether or not they all existed at the same time is unclear, especially as the Beanish appear to be rather long-lived (the Beanish Bubbles having been alive for more than 1000 years), but their spheres of influence can be tracked in the modern day at least.