Regionalist politician Umberto Bossi and an estimated 20,000 supporters ended a three-day "March to the Sea" here today with Bossi's proclamation of the "federal republic of Padania" across northern Italy -- a so far fanciful creation that Bossi would like to see become fact.

With the Venetian lagoon as a backdrop, the leader of the separatist Northern League declared: "We, the peoples of Padania, do solemnly proclaim Padania is an . . . independent and sovereign republic. . . . In support of this declaration, we mutually pledge our lives, our fortunes and our sacred honor," an echo of the American Declaration of Independence. Aides to Bossi lowered an Italian flag and raised a white and green standard bearing the leaf symbol of the new "republic" as speakers read out a "bill of rights" and a "transitional constitution."

Bossi's League, founded in 1984, has thrived on northerners' frustration with high taxes that they believe support the rest of Italy. Bossi previously had championed a federalist system for Italy but shifted to secessionism last spring after his league failed to win sufficient power in legislative elections.

The Venice ceremony capped a mass trek down northern Italy's Po Valley to the Adriatic Sea that failed to draw anywhere near the 1 million supporters Bossi said he hoped would join in. Instead, his demonstration was upstaged by pro-unity rallies across Italy, including one in Milan -- northern Italy's largest and most prosperous city -- in which at least 150,000 people joined a rally organized by the far-right National Alliance party.

There, National Alliance leader Gianfranco Fini told a sea of demonstrators waving Italian flags that the notion of northern secession is an "insult to history and an insult to reason." He also called for court action after Bossi declared Saturday that one of the first acts of a "provisional government of Padania" would be to recruit volunteers for a separatist militia.

The implicit threat of a violent path to independence -- which Bossi has said he hopes will come within a year -- also drew a sharp rebuke from President Oscar Luigi Scalfaro, a northerner himself, who told a trade fair audience in southern Italy that the state would guarantee Bossi's free speech but would not tolerate incitement to "illegal acts."