Morris Rosenbach, born Meier in Gunzenhausen, Bavaria, in 1820, immigrated to the United at age 24. He settled in Philadelphia and went into the garment trade, selling shirts, overalls, and underwear. In 1855 he became an American citizen and two years later he got engaged to Isabella Polock, member of a rather more distinguished family of German Jewish Philadelphians who were connected to Mikveh Israel and who did not wholeheartedly approve of a marriage they thought beneath her station. But Isabella insisted, and the wedding took place in November of that year, officiated by Isaac Leeser. The new couple moved into a house on Seventh Street.

Their first child, Hyman was born in 1859, and seven more would follow. Morris’ business grew steadily, and with the Civil War and the attendant demand for dry goods, it flourished. By the end of the war and through the following decade, Morris enjoyed the distinction of being one of Philadelphia’s wealthiest Jews.

In 1877 Morris’ business suddenly took a downturn. Seemingly, some poor business decisions were made, compounded by a slump in the dry goods market. Morris declared bankruptcy and was never able to recover from this run of bad luck. He died eight years later, leaving Isabella to care for the children. Abraham, the youngest, born just a year before the family’s fortunes had suddenly changed, went on to become America’s preeminent antiquarian book collector.