1859 Prussia, German States, Germany, Folded Letter with Prussian Closed Mail Service to the United States, Red Transit and Arrival Postmark

 This item from 1859 is a fascinating example of transatlantic postal history. It is a letter sent from Germany to California via Prussian Closed Mail.

The folded letter started from Potsdam (Prussia) with departure postmark December 10th. It arrived at the exchange office in Aachen on December 11 (red double-circle stamp "25 ct. Paid"). Aachen was the Prussian exchange office for mail to the USA. The "AACHEN / PAID / 25" postmark is a crucial accounting mark from the Prussian-U.S. Postal Treaty of 1852.

It traveled via Belgium and England to catch a British Packet (Cunard Line) steamship. It reached New York on December 30, where it received the red "30 / DEC / 28 / PAID / BR. PKT." arrival postmark.
The "30" in the New York postmark indicates the 30-cent rate for a 1/2 ounce letter. Due to the "25ct.Paid" in the red Aachen postmark it means that 5ct kept by Prussia (to cover German inland postage) and 25cent were credited to the United States