Why can't I define an array size using #define constant?

Question

Method 1: works

const int MAX_STRING = 256;

int main(void) {
    char buffer[MAX_STRING];
}

Method 2: Does not work - compilation error.

#define MAX_STRING 256;

int main(void) {
    char buffer[MAX_STRING];
}

What is the reason of the different behavior of those codes? Are those both MAX_STRINGs not constants?