Building roads on every square in the city radius of the Colossus will help maximize the trade output. It can also be very helpful to build Copernicus' Observatory in the same city.
The Colossus of Rhodes was a bronze statue of Helios, the God of the Sun, erected near the city harbor. It stood over 100 feet high, about two-thirds the height of the Statue of Liberty. Unfortunately, it was knocked down by an earthquake only 56 years after its construction. Taking the counsel of an oracle, the city elected to leave the statue where it lay, and it stayed there for 900 years until sold for scrap by Muslims who plundered the city in 654 A.D. Travelers from all over the ancient world came to Rhodes to see the Colossus, both when it stood and after it fell.