The word nimpu simply means "worker" or "coolie", but in this case it refers to men who travel up and down the highway on foot carrying packs of goods.
In addition to the average laborers who carry goods, parcels and produce, there are also special messengers who carry the mail. Although normal messages are sent by the horse messenger service, secret messages and "classified" documents are usually sent by foot. It is safer and only a little bit slower than the horse service. The fellows who carry messages are known as hikyaku. Literally, that means "flying feet" in Japanese, but it is best translated as "foot messenger".
There are several types of hikyaku. The ones who carry messages from the Shogun and the Emperor are on call 24-hours a day, and they are called tsugi-hikyaku, or "continuous messengers". Those that carry messages for the average merchant or bureaucrat are known as sando-hikyaku ("three-times" messengers) because they make deliveries only three times a month. Finally, there are machi-hikyaku (city messengers) who can be hired from a shop that specializes in this service, known as a hikyaku-ya