History of the Peloponnesian War

Thucydides

Thucydides. The Peloponnesian War. London, J. M. Dent; New York, E. P. Dutton. 1910.

With the beginning of the winter following Ramphias and his companions penetrated as far as Pierium in Thessaly; but as the Thessalians opposed their further advance, and Brasidas whom they came to reinforce was dead, they turned back home, thinking that the moment had gone by, the Athenians being defeated and gone, and themselves not equal to the execution of Brasidas' designs.

The main cause however of their return was because they knew that when they set out, Lacedaemonian opinion was really in favour of peace.