Final answer:
The development of a chancre marks the primary stage of syphilis, characterized by a firm, painless sore at the infection site, lasting 3 to 6 weeks.
Step-by-step explanation:
A chancre develops during the primary stage of syphilis. This stage is the initial phase of the infection and is characterized by at least one chancre, which is typically firm, round, and painless. The chancre appears at the location where the syphilis bacteria entered the body and signifies the body's reaction to the infection.
It usually lasts from 3 to 6 weeks and heals regardless of whether or not the person receives treatment, although the absence of a visible chancre does not mean the infection has cleared without medical intervention.