Charleston, South Carolina:

Industries slowly brought the city and its inhabitants back to a renewed vitality and jobs attracted new residents. As the city's commerce improved, residents worked to restore or create community institutions. In 1865, the Avery Normal Institute was established by the American Missionary Association as the first free secondary school for Charleston's African American population. General William T. Sherman lent his support to the conversion of the United States Arsenal into the Porter Military Academy, an educational facility for former soldiers and boys left orphaned or destitute by the war. Porter Military Academy later joined with Gaud School and is now a university-preparatory school, Porter-Gaud School.

Please answer a question about this article. If the question is unanswerable, say "unanswerable". What type of school was the Avery Normal Institute?
free secondary school