sentences:  In 1819, military architect Jan Bernhard planned and started the construction of "Aleja Najświętszej Panny Marii"—the "Holy Virgin Mary Avenue", which is currently the main arterial road of the modern city, and which connected Old Częstochowa with New Częstochowa.Finally, both towns were officially merged on August 19, 1826.The new city quickly emerged as the fourth-largest urban centres of Congress Poland; larger were only the cities of Warsaw, Lublin, and Kalisz.