The reason behind the use of fish, on the other hand, is simple: Christmas Eve is a vigilia di magro, in other words, a day of abstinence in which the Catholic Church prohibits the consumption of meat. Though this stricture is less observed now, in the past it meant that everyone would crowd the fish market on Christmas Eve, and Livio Jannattoni gives a wonderful description of the society dons and their dames gliding between the tubs of slithering eels and tables of shellfish and other delicacies in the Roman fish markets of the 20s, their elegant clothing and fine shoes contrasting oddly with the cold wet floors and the gruff fishmongers bent on making deals. Speaking of Naples, on the other hand, Caròla Francesconi writes, in La Cucina di Napoli, "The week before decisions are made regarding the three Christmas dinners, Christmas Eve, Christmas and Prima Festa (the 26th). The Christmas Eve dinner is more traditional than the others and must include:"
- Drowned broccoli rabe (also known as Christmas Broccoli)
- A choice of:
- Vermicelli Aglio e Olio
- Vermicelli with Anchovies
- Vermicelli with Clams (add the tomatoes)
- Roasted or fried eel, followed by other fish dishes of choice, which could range, depending upon the depth of the wallet, from humble baccalà to baked fish or luxurious lobster.
- A refreshing caponata di pesce (fish salad) to wrap up the main dishes.
- Christmas desserts: paste reali, susamielli, rococò and mustacciuoli, sometimes accompanied by nut crunch. And finally, dried fruit (dates, figs, nuts, and la collana del prete (the priest's necklace), chestnuts strung together).
The Christmas day menu, she notes, is much freer -- baked pasta, either lasagna or a timpano, roasts -- fish for those who like it and capon or turkey, caponata, and dessert. The only requirement is Struffoli.
Even freer is the third of the dinners, on December 26th, which some people begin with tagliatelle with a ricotta-based ragú, and others do not.
One important thing to note about Ms. Francesconi's menu suggestions is that she doesn't specify the number of dishes to be served -- this will vary depending upon the number of people partaking. Another is that she mentions only traditional Neapolitan Christmas pastries. Modern marketing is a powerful force, and now, in addition to the traditional desserts you will almost certainly find either panettone or pandoro, and possibly panforte.
Panettone is a Milanese specialty bread made with raisins and candied fruit that keeps quite well, so well that Milanese tradition dictates a slice of the Christmas panettone be set aside for San Biagio, which is in mid-February; Pandoro is a airy, buttery Christmas cake from Verona; Panforte is an ancient Sienese variation on fruitcake, made with almonds, honey, flour and candied fruit. It's heavenly, though a little goes a long way.

