This section of the book is from the "Introduction To Public Finance" book, by Carl Copping Plehn.
Customs duties are taxes levied upon commodities when they cross the national boundary line, or are admitted within a customs territory, consisting of a combination of countries or of definitely limited parts of countries. Unless a city or town forms an independent sovereignty, taxes levied on goods entering a city are not called customs duties, but octroi or imposts, and partake of the nature of excises. Duties upon goods passing from province to province in the same country are likewise not customs duties. Neither are tolls or transit duties charged upon goods passing through the country. Such charges are fees for the ostensible or real service of the government in keeping up roads and bridges, maintaining peace, and allowing transit.1 Customs duties are indirect consumption taxes of practically the same character as excises. Their treatment in a separate chapter is not on account of any actual difference in nature but because of their historical and fiscal importance.
1 Cf. Bastable, p. 513, for contrary view. Bastable does not recognise fees as a separate class. Hence his identification of transit duties with customs duties.