began publishing in an independent Catholic weekly Tygodnik Powszechny. It was then that he took the pen-name Jasienica (from the name of the place where he had received treatment for his injuries) in order not to endanger his wife, who was still living in Soviet-controlled Vilnius, Lithuania. Soon he became a member of the weekly's staff and then an editor. In 1948 he was arrested by the Polish secret police () but after several weeks was released after the intervention of Bolesław Piasecki from the PAX Association. In gratitude to Piasecki, thereafter he worked with PAX, leaving Tygodnik Powszechny for PAX in 1950. In 1950, he became a director of the Polish Caritas charity. Jasienica became a member of the Crooked Circle Club, which espoused free speech and open discussion. His essays were published in Dziś i Jutro, Słowo Powszechne, Życie Warszawy, Po Prostu. From at least this period until his death he would live in Warsaw. His wife Władysława died 29 March 1965. Over time, he became increasingly involved in various dissident organizations. In December 1959, he became a vice president of the Union of Polish Writers (Związek Literatów Polskich, ZLP). He also published in the magazine Świat (1951–1969). In 1962 he was the last president of the literary discussion society, Crooked Circle Club. In 1966 he was a vice president of the PEN Club. While in the late 1940s and 1950s he focused mostly on journalistic activity, later he turned to writing popular history in book format. In the 1960s he wrote his most famous works, historical books about history of Poland – the Kingdom of Poland in the times of the Piast dynasty, the Jagiellonian dynasty, and the era of elected kings (the Polish–Lithuanian Commonwealth). His book on Jagiellonian Poland was recognized as the best book of the year by the readers. Jasienica was, however, very outspoken in his criticism of the censorship in the People's Republic of Poland. On 29 February 1968 during a ZLP meeting, Jasienia presented a harsh critique of the government. These acts, and in particular his signing of the dissident Letter of 34 in 1964 against censorship and his involvement in the 1968 protests led to his being labeled a political dissident, for which he suffered government persecution. Partly as a response to government's persecution of Jasienica, in 1968 the satirist Janusz Szpotański dedicated one of his anti-government poems, Ballada o Łupaszce