About 1231, he sculptured at Bologna the urn of San Domenico, and from this, as a remarkable event, he was named "_Niccola of the Urn_." He afterwards executed in a much superior style, the Last Judgment, for the cathedral of Orvieto, and the pulpit in the church of San Giovanni, at Pisa; works that demonstrate to the world that design, invention, and composition, received from him a new existence. He was succeeded by Arnolfo Florentino, his scholar, the sculptor of the tomb of Boniface VIII. in San Pietro at Rome; and by his son Giovanni, who executed the monuments of Urban IV. and of Benedict IX. in Perugia. He afterwards completed the great altar of San Donato, at Arezzo, the cost of which was thirty thousand gold florins; besides many other works which remain in Naples and in several cities of Tuscany. Andrea Pisano was his associate, and probably also his disciple in Perugia, who, after establishing himself in Florence, ornamented with statues the cathedral and the church of San Giovanni in that city; and in twenty-two years finished the great gate of bronze "to which we are indebted for all that is excellent, difficult, or beautiful in the other two, which are the workmanship of succeeding artists." He was, in fact, the founder of that great school that successively produced Orcagna, Donatello, and the celebrated Ghiberti, who fabricated those gates for the same church, which Michelagnolo pronounced worthy to form the entrance of Paradise. After Andrea, we may notice Giovanni Balducci, of Pisa, whose era, country, and style, all lead us to suppose him one of the same school. He was an excellent artist, and was employed by Castruccio, Lord of Lucca, and by Azzone Visconti, Prince of Milan; where he flourished, and left, among other monuments of his art, the tomb of San Pietro Martire, at S. Eustorgio, which is so highly praised by Torre, by Lattuada, and by various other learned illustrators of Milanese antiquities.[35] Two eminent artists, natives of Siena, proceeded from the school of Gio. Pisano, namely, the two brothers, Agnolo and Agostino, who are greatly commended by Vasari as improvers of the art. Whoever has seen the sepulchre of Guido, bishop of Arezzo, which is decorated with an infinity of statues and basso-relievos, representing passages of his life, will not only find reason to admire in them the design, which was the work of Giotto, but the execution of the sculpture. The brothers also executed many of their own designs in Orvieto, in Siena, and in Lombardy, where they brought up several pupils, who for a long period pursued their manner, and diffused it over Italy.