 During his tenure, the diocese of Richmond and Charleston were created.The building of the Baltimore Basilica, the first Catholic Cathedral built in the United States, which had been begun under Archbishop John Carroll in 1806, was now resumed and completed and was dedicated on May 31, 1821, under the title of the "Assumption of the Blessed Virgin Mary".Also in 1821, Maréchal went to Rome on business of his diocese, and in connection with the White Marsh plantation which the Archbishop claimed as Diocesan property, but which had been given to the Jesuits on February 17, 1728, and was claimed by them as property of the Society to be employed in the interests of the Church of Maryland.