Almost all are in the baroque style and were installed in the 17th, 18th, and 19th centuries, although a few date all the way back to medieval times and a few are fairly recent. They often have only a small image dwarfed by a grandiose frame featuring expanding rays of light and sometimes stucco angels and putti (infant angels). Some have canopies to protect them from the elements, and there is often also a small light stand (some recently electrified) and a place for flowers and offering. Many are high on the walls, but a few are at eye level.
Up until a few years ago most of the Madonnelle were neglected, and almost all had blended into the uniform gray/black of building fronts and corners -- urban pollution made those behind glass fronts totally invisible. But, in the general cleanup before the 2000 Jubilee, some were cleaned with the buildings to which they are attached, and others were cleaned independently using funds made available by the Comune di Roma (city hall) and by the Vatican. Several hundred are now visible for the first time in living memory.
Being able to see the Madonnelle, however tells you nothing about what they mean or who established them. Much of this information died at the end of the generations of the founders, but some facts are known, and there are places to go on the Internet (of course) to find them. The best place to go is http://www.photoroma.com/sezioni/archivi/madonnelle.htm where you can find links to pages documenting more than 130 of the more picturesque Madonnelle. They are sorted by region in the city and the street they are on (but not the exact address), and whatever is known about the individual shrine is given in tabular form. The web site is in Italian, but it is easily deciphered. (The Madonnelle pages are, in fact, only a small part of the Photo Roma Internet site, which currently has more than 1700 Rome photos in its archive -- more are added periodically. For links, go to http://www.photoroma.com.)
There have been occasional "manifestations" (miracles or mass hysteria, take your pick) associated with the Madonnelle, and the most widespread, involving several of the Madonnelle, occurred in July of 1796. Official inquiries at the time recorded that the eyes of Madonnelle in several parts of the city were seen to move. Measurements, taken on some Madonnelle while the eyes were moving, seemed to confirm the miracle. The eye movements were taken as an evil omen.
And there was good reason to believe that evil was immanent: a few months earlier, Napoleon had arrived in northern Italy for his first Italian campaign, and his war there against the Austrians, who, at the time, were the nominal protectors of Rome and the Papal States, had already begun. Within two years there were French troops Around Rome. The Church quickly certified the Madonnelle miracles and some of the shrines were moved inside neighborhood churches, which were then renamed in their honor. Within another three years Napoleonâs second Italian campaign had totally defeated the Austrians, Rome was taken, and the Concordat of 1801 formalized French domination of the Papal States which lasted until 1870 when the French garrison was needed for the Franco-Prussian war and the Bersagliari took the undefended city, finally unifying Italy. For more on the 1896 "miracles" and other Madonnelle manifestations, go to http://www.geocities.com/Paris/Arc/5319/roma-c13.htm.
The Ancient Connection: As with almost everything in Rome, there is an "Ancient Roman" connection. The first Madonnelle, on building corners above urban intersections. were actually early Christian replacements for pagan shrines dedicated to the Lares Compitales (minor gods of the crossroads). A one-day annual festival around the first of January and called the Compitalia (Crossroads Festival) recognized these minor and very local gods. At first it was a rural observance that may have involved verifying and rectifying (straightening) farm boundaries by marking them out with plowed furrows. Where furrows intersected shrines to the Lares were erected, and as time went on the furrow/boundaries became footpaths and then roads. Eventually there were annual sacrificial meals and festivals at the crossed boundaries/crossroads, and, later, games and other religious observances were added.
Octavian (Caesar Augustus) urbanized the festival by dividing Rome into 265 "vici" (neighborhoods) and ordered the erection of shrines at intersections of streets between them. The crossroad gods acquired two additional urban names, "Lares Vicinali" and "Lares Augusti", and the festival was lengthened to three days. The rural to urban shift recognized the shift of Italian population to Rome and to other cities where similar plans were soon instituted. More importantly, it established a religious foundation for Octavianâs administrative reforms in the cities: although most Romans had long since become blasé about the transplanted Olympian gods, they scrupulously and superstitiously clung to the minor league Lares observances, so that is what Octavian exploited. In the process he also established the tradition, which is perpetuated in the Madonnelle, of street-corner shrines in Rome and other Italian cities.
P.S.: Lares were, in popular belief, everywhere and of many kinds besides the Lares Compitales: they inhabited every implement and utensil, every structure and even parts of structures (left and right door-posts and door lintels each had their own, for example), every place or thing. There were myths that said they were the children of the unwilling nymph Lara and one of the Olympians, but Roman folk believed unanimously that they were the souls of their own good ancestors. Lares were therefore good spirits, but you had to stay on their good side. If you didn't, they might abandon you and then the corresponding bad guys, souls of the evil dead called Larvae, would have a clear shot at you. There were also Lemurs to contend with -- ghosts of either good or bad people, who were just unsettled and angry because they didnât get proper funeral rites.
More Internet links:
Compitalia, Smith Dictionary of Greek and Roman Antiquities: http://www.ukans.edu/history/index/europe/ancient_rome/E/Roman/Texts/secondary/SMIGRA*/Compitalia.html
"Lares" from Encyclopedia Mythica: http://www.pantheon.org/mythica/articles/l/lares.html
Google Directory of Roman gods, from Encyclopedia Mythica: http://directory.google.com/Top/Reference/Encyclopedias/Subject_Encyclopedias/Encyclopedia_Mythica/Roman/