Rutter (nautical)

A rutter is a mariner's handbook of written sailing directions. Before the advent of nautical charts, rutters were the primary store of geographic information for maritime navigation.

It was known as a periplus ("sailing-around" book) in classical antiquity and a portolano ("port book") to medieval Italian sailors in the Mediterranean Sea. Portuguese navigators of the 16th century called it a roteiro, the French a routier, from which the English word "rutter" is derived. In Dutch, it was called a leeskarte ("reading chart") and in German a Seebuch ("sea book").

Before the advent of nautical charts in the 14th century, navigation at sea relied on the accumulated knowledge of navigators and pilots. Plotting a course at sea required knowing the direction and distance between point A and point B. Knowledge of where places lay relative to each other was acquired by mariners during their long experience at sea.

The earliest peripluses of classical antiquity were not necessarily written as practical navigational handbooks. Some were more akin to an adventure travelogue, to celebrate a famous voyage. Others were disguised as such, notably the Periplus of Pseudo-Scylax from the 4th century BCE, which described the harbors and landmarks along the north African coast west of the Nile delta. Still others were designed as commercial guides for merchants, such as the Periplus of the Erythraean Sea, written around 100 CE by a Greek merchant in Egypt, as a guide to the market ports of the Red Sea and Indian Ocean.

The re-emergence of maritime commerce in the Mediterranean Sea during the Middle Ages (12th–13th centuries), spearheaded by Italian ports like Amalfi, Pisa, Genoa and Venice, led to the rise of a new set of handbooks, known as portolani ("port books"), designed for the practical use of mariners. These were likely first compiled by professional mariners and pilots, probably as a mnemonic set of notes for their own personal use. These notes were probably passed secretly within their profession ranks, from master to apprentice. Only a few of these Italian handbooks were made public, and even fewer have survived to this day. The most complete surviving portolano is the famous Il compasso da navigare, written c. 1250 and published in Genoa in 1296.

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