Year 423 BC was a year of the pre-Julian Roman calendar. At the time, it was known as the Year of the Consulship of Atratinus and Ambustus (or, less frequently, year 331 Ab urbe condita). The denomination 423 BC for this year has been used since the early medieval period, when the Anno Dominicalendar era became the prevalent method in Europe for naming years.
The Athenian general, Laches, successfully moves in the Athenian Assembly for an armistice with Sparta to check the progress of Sparta's most effective general, Brasidas. However, the "Truce of Laches" has little impact on Brasidas and collapses within a year.
Brasidas ignores the proposed year-long truce and proceeds to take Scione and Mende in the hope of reaching Athens and freeing Spartan prisoners. Athens sends reinforcements under Nicias who retakes Mende.