As mentioned, an array of servos.
Some completely untested code that illustrates the process
#include <Servo.h>
const int NumServos = 4;
Servo ServoArray[NumServos];
int ServoPins[NumServos] = {7, 8, 9, 10};
void setup() {
// put your setup code here, to run once:
for (int i = 0; i < NumServos; i++)
ServoArray[i].attach(ServoPins[i]);
}
void loop() {
// put your main code here, to run repeatedly:
for (int i = 0; i < NumServos; i++)
{
for (int j = 0; j < 180; j++)
{
ServoArray[i].write(j);
delay(20);
}
}
}