Read the selection and answer the question.

The Colosseum

Imagine being in Rome $1900$ years ago. Huge crowds of people hurry down the street toward you, filled with excitement. They are going to see a battle of gladiators at the Colosseum, and the show is about to begin.

Gladiator battles were among the many spectacles that took place in Rome's Colosseum. The structure was a large oval similar to baseball and football stadiums of today. This remarkable arena was built almost $2000$ years ago and was used for almost four centuries.

Construction of the Colosseum began in $72$ A$.$D$.$ during the rule of the Roman Emperor Vespasian. It was completed eight years later by Vespasian's son, Titus. The Flavian Amphitheater, as it was first called, stood $157$ feet high. It was $620$ feet long and $513$ feet across. There were $80$ entrances around the base: $76$ for spectators, two for participants in the games, and two just for the emperor and his family. As in modern sports arenas, there were different seating levels. The ringside box seats were reserved for important officials. Lower level seats cost more than the upper level seats. Historians believe that the Colosseum could hold $45,000$ people. $($That$\text{'}$s bigger than Boston's Fenway Park, which holds $34,000$ Red Sox fans.$)$ It even had a system for drawing a large awning over the seating area to protect spectators from the hot sun.

The inside oval was $287$ feet long and $180$ feet wide, making it about the size of a modern$-$day football field. It was the largest arena space in the world at that time. This area was built of wood and covered with sand. Beneath it lay a maze of hallways, rooms, and holding pens that held all of the elaborate decorations and props used in the shows. This arena space could also be flooded with water in order to stage battles with boats!

Spectators at the Colosseum often saw violent, bloody shows, and some events lasted all day. Sometimes men hunted wild animals, such as lions and tigers. Duels between gladiators began early in the day with wooden weapons. Battles to the death took place later in the day.

Then in $312$ A$.$D$.,$ Constantine I became the first Christian emperor of Rome. Under his rule, the shows at the Colosseum became less violent. People began to question whether it was right to hunt animals and hold battles for entertainment.

The last known event in the great arena took place in $404$ A$.$D$.$ By that time, the Roman Empire was falling apart and excited crowds no longer filled the stadium. The Colosseum has stood at the center of the city through many centuries since then and can still be seen today.

The author's main purpose in this selection is to$$

A

explain why the Roman Empire collapsed.

B

give information about the Roman Colosseum.

C

describe the life of a gladiator in Rome.

D

compare Constantine with other Roman emperors.