The April 20 Mass at Yankee Stadium will mark the bicentennials of the archdioceses of New York, Boston, Philadelphia and Louisville, Ky., which was founded as Bardstown, Ky.

The four dioceses, before being named archdioceses, were erected in 1808 from the Baltimore Diocese, the nation’s first diocese, which became an archdiocese that year. The coats of arms of the five archdioceses will be displayed in right, left and center fields at the stadium.

Their archbishops are scheduled to be concelebrants at the Mass; they are: Cardinal Edward M. Egan of New York, Cardinal Sean P. O’Malley of Boston, Cardinal Justin Rigali of Philadelphia, Archbishop Joseph E. Kurtz of Louisville, Ky., and Archbishop Edwin F. O’Brien of Baltimore.

The New York, Boston, Philadelphia and Louisville archdioceses have been marking their bicentennials with yearlong celebrations including special liturgies, youth gatherings and programs of spiritual renewal.

But in the beginning, there was just Baltimore.

Baltimore, and the wider Maryland colony, was the Catholic homeland in a young nation that was largely Protestant, yet was to be shaped by the waves of Catholic immigrants who transformed cities such as New York, Boston and Philadelphia, among others.

The massive Baltimore Diocese led by Bishop John Carroll initially included the entire United States. The move by Pope Pius VII to make four smaller dioceses illustrated that “the church was becoming a permanent part of the American scene,” Father Clyde Crews, a historian at Bellarmine University in Louisville, told Catholic New York, the archdiocesan newspaper.

Tricia Pyne, archivist for the Archdiocese of Baltimore, noted that Bishop Carroll had for years requested the establishment of separate dioceses in the new nation.

The Louisiana Purchase of 1803 doubled the size of the new nation and Catholic settlers clamored for more priests. Rome, preoccupied with European strife, was slow to respond, she added, while the Napoleonic wars and the glacial pace of news slowed events until the 1808 creation of the new dioceses.

Bishop Richard Luke Concanen, a Dominican, was named the first bishop of New York, but was unable to leave Europe because of the Napoleonic wars. The administration of the new diocese fell instead to Jesuit Father Anthony Kohlmann, vicar general for the diocese.

Among his accomplishments, Father Kohlmann supervised the plans for what is now St. Patrick’s Old Cathedral, which upon its completion in 1817 was the largest church building in the city.

Father Kohlmann is perhaps best known for his defense of the seal of confession, a struggle that culminated in historic New York state legislation offering legal support to the confidentiality of the sacrament.

According to Father Crews, the most prominent of the new dioceses in 1808 may well have been Bardstown. It was before large-scale immigration and the Catholic communities in East Coast cities such as New York, Boston and Philadelphia remained relatively small.

But Kentucky, then being settled by a large number of Catholics from Maryland, became a center of Catholic life, even in its unlikely frontier setting. Bishop Benedict Joseph Flaget, a refugee from the French Revolution, became the first bishop of Bardstown and became known as “the first bishop of the West.”

He led a see that included Kentucky, Tennessee and what later became Indiana, Ohio and Illinois. More than 40 modern dioceses have been carved out of what was the Diocese of Bardstown, which moved to Louisville, a much larger city, in 1841.

The three counties around Bardstown became known as the “Holy Land” among Kentucky Catholics because of the relatively high percentage of Catholics, Father Crews said. The area boasts a number of motherhouses for sisters, as well as the famous Gethsemani Monastery, a Trappist institution founded by French monks.

Father Crews, a priest of the Louisville Archdiocese, noted the New York connection to the area: A New Yorker, Trappist Father Thomas Merton, became Gethsemani’s most famous monk in the mid-20th century.

During a Mass to open the bicentennial year of the Archdiocese of Boston, Cardinal O’Malley urged disillusioned Catholics to “come home” to the faith.

The cardinal, fully aware of efforts to rebuild trust among Catholics in the wake of the clergy sex abuse crisis and parish and school closings in the Boston Archdiocese, recounted the difficult beginnings of the archdiocese in an area of the country where anti-Catholic sentiment was widespread and often backed by the force of law.

When the archdiocese was founded 200 years ago, “the entire Catholic population of the diocese would not have filled this church,” he said during a Dec. 2, 2007, homily at the Cathedral of the Holy Cross in Boston. “There were about 1,000 Catholics and two priests,” he added. “Those handful of Catholics of two centuries ago, have grown to over 5 million Catholics in New England today.”

In opening remarks for the Archdiocese of Philadelphia’s bicentennial celebration, Cardinal Rigali noted the archdiocese has a history rich in immigrants, the establishment of the Catholic school system and Sts. John Neumann and Katharine Drexel.

“Much has changed in geography, structure and in the number of parishes, schools and other agencies over two centuries,” he said. “Throughout the years, however, one witnesses constant devotion to Our Lord Jesus Christ by the clergy, religious and laity.”