Today, stamps are a fundamental part of mailing letters. It wasn’t always that way, though. Originally, letters were taken to the local postmaster, who counted the number of pages and the distance the letter had to travel to determine the postage, which was then written in the upper right corner. If the sender paid the postage, the word “PAID” was written there as well. If the sender didn’t pay for the letter to be sent, the recipient was expected to pay on delivery.

Stamps were first developed in the 1840s. They were printed on unperforated sheets that had been covered with adhesive gum on one side. Clerks had to cut them off the sheet with scissors. This proved to be impractical, though, and soon someone developed the idea of perforating sheets of stamps, making them easier to remove.

Stamps proved to be popular. So popular, in fact, that the Post Office started experimenting with ways to make it easier for customers to buy and use them. So, on April 16, 1900, the Post Office offered its first books of stamps for sale. They came in three sizes, containing 12, 24, or 48 stamps each. Because the adhesive gum was so sticky, they had waxed paper placed between the sheets to keep them from sticking to each other. They had cardboard covers with postal rates printed on them.