Pictorial postmarks are also known as Special Handstamps/Postmarks. Cachets, which should not be confused with postmarks, are basically rubber stamps. Czarist Russian postmarks and stamps were in used in the territory of Armenia from 1858. Some historians also consider these postmarks to be the world's first postage 'stamps'. The study of postmarks is a specialized branch of philately called marcophily. With postmarks becoming more and more important to the covers, pictorial postmarks became very popular. Dated postmarks with city names soon followed. These include the so-called fancy cancels of United States to modern machine postmarks. No TPO postmarks are known for other railway lines. Consequently, many blockade covers have postmarks from these locations. Portuguese postmarks are known from 1854 when a post office was opened in Goa. Different types of postmarks include railway post offices ("RPOs") and maritime (on-board ship) postmarks. Wilhelm Klein noticed a good continuity in many postmarks on the last issues in kreuzer.