Cut the wild boar meat into bite-sized pieces.
Place the meat in a large container with a lid. Add roughly chopped celery, carrot, and onion, along with the red wine, bay leaves, rosemary and sage and crushed juniper berries, garlic and black peppercorns.
Cover and refrigerate overnight to marinate.
The next day, drain the wild boar thoroughly in a colander, discarding the marinade and all aromatics.
Finely chop and mash fresh celery, carrot, and onion.
Heat olive oil in a large casserole. Add crushed garlic, the chopped vegetables, bay leaves, sage, rosemary, and juniper berries. Sauté over high heat.
Once the onion becomes lightly golden, add the wild boar and brown it thoroughly, stirring frequently until all moisture has evaporated and the meat is well browned. This may take around 30 minutes.
Add the red wine and let it completely evaporate.
When the meat starts sizzling again and begins to stick slightly to the bottom of the pot, add the peeled tomatoes (or passata) and the drained bitter brined olives.
Once the tomatoes are fully incorporated and the mixture begins to sizzle again, pour in enough boiling hot water to nearly cover the meat.
Cover with a lid, reduce the heat to low, and simmer gently for about 3 hours, adding more hot water if necessary to keep the stew moist.
Remove the garlic, rosemary sprigs, and bay leaves before serving.