Laurie burst into Grandpa's study, blowing on a paper noisemaker.
"Grandpa, will you come downstairs to watch the countdown with us?"
It was New Year's Eve, and Grandpa had been in his study since after dinner.
"Of course! Is it that time already?" Grandpa said.
"Yep. It's almost 2011!" Laurie looked at the calendar hanging on the wall. "You need a new calendar!"
"I always find it amazing that humans have been on Earth for well over ten thousand years, but our calendar only says 2011!" Grandpa said.
"What year is it really?" Laurie asked, confused.
"It depends on when you start your calendar.
Most of the world uses a calendar that begins with the birth of Jesus Christ.
Every year before that is marked with 'BC,' which stands for before Christ.
Every year after that is marked by 'AD,' which stands for the Latin words anno Domini, meaning in the year of the Lord.
Before Jesus, most calendars were based on the cycles of the moon or the sun, or both.
It was also common to count years based on the start of a leader's or dynasty's rule.
But Jesus changed the world. In the sixth century, a monk created a calendar that began with the birth of Jesus."
"So the birth of one man changed the way humans record time?" Laurie asked.
"Yes. And not only that. His life and death also gave rise to the largest religion in the world—Christianity."
"I only know a little about Jesus from the stories around Christmas time."
Laurie glanced at the clock. It was 11:46 p.m.
"What was so special about his life?"
"I'll tell you as much as I can—but quickly, because I know Mom and Dad are waiting for us.
Jesus was born in Bethlehem, a Jewish city that was part of the Roman Empire.
He was the son of a carpenter named Joseph and a woman named Mary, who raised him in the Jewish tradition.
Many people believed he was the leader who would free the Jews from Roman rule.
Others thought he was the son of God.
Anyway, Jesus studied Judaism carefully and became a preacher.
He preached about love, heaven, and the forgiveness of sins.
He wanted to tell people everywhere that God loved them.
Now, although Jesus worshipped the same god as the Jews, his teachings strayed from traditional Jewish beliefs.
So some Jews accepted him, but many others did not.
And the Romans didn't bother him, because they generally allowed their subjects to follow different religions as long as no one harmed the state.
As Jesus gained more and more followers, however, many Jews and Romans began to worry about his power.
When Jesus was just 33 years old, a Roman official ordered him to be killed.
But even after his death, Jesus' followers kept believing in what he had said, and Christianity arose.
At first this religion was practiced by only a small number of people, and not many others understood it.
But as Jesus' followers journeyed to tell others about their new faith, Christianity spread throughout the Mediterranean world.
These early Christians weren't treated very well in the Roman Empire.
Roman emperors often held ceremonies related to Roman gods and goddesses. They wanted all their people to participate.
But Christians believed in a single god and wouldn't take part in anything related to Roman gods.
So some Roman leaders saw Christians as a threat because they obeyed their faith rather than the Roman emperor.
These Romans persecuted Christians. But Christianity continued to gain popularity because it gave people hope.
Christians spoke of life after death, when people would live in the kingdom of God.
They also said that all people were equal before God.
This included everyone—from emperors to commoners."
"So I guess common people liked the religion, but the emperors didn't?" Laurie asked.
"Right. Not at first anyway. But in 312 AD, the Roman emperor Constantine converted to Christianity, and persecution of the Christians ended.
In 380 Emperor Theodosius made Christianity the empire's official religion, creating the world's first Christian empire.
Gradually Christians began settling in large communities and building churches.
Bishops, who were the heads of churches, became more powerful.
In big cities, such as Rome, their authority extended from religion into politics.
Once Christianity gained the approval of Roman emperors, it grew and grew within the empire.
Churches were built using state money. Courts run by churches appeared, and they soon held more power than the Roman government over religious issues.
The bishops of Rome, known as popes, became especially influential.
They claimed authority over all other churches.
At the same time, the Roman Empire was being attacked by nomadic troops from Europe and Asia.
As the state grew weaker and Christianity grew stronger, people found more security with the church than they did with the state.
Soon Christianity spread beyond the Roman Empire.
Part of Jesus' message was that God was universal, so Christians believed they should spread Jesus' teachings throughout the world.
Roman roads and access to the Mediterranean Sea made it easy for Christians to go on missions.
Christians moved north throughout Europe and converted the people there.
By the time the Roman Empire reached its last days around 500 AD, Christianity had become the dominant religion in Europe.
And that brings us to the eve of the Middle Ages, Laurie, when the Christian church and the pope became the supreme authority on nearly everything."
"The eve of the Middle Ages? Grandpa, it's the eve of 2011 and here we are sitting and talking about stuff that happened over 1,500 years ago!
Let's go downstairs and celebrate what's happening now!" Laurie grabbed Grandpa's hand.
"Okay. You have a point," Grandpa said, standing up. "I should stop rambling."
"Happy 2011, anno Domini!" Laurie cried as they walked out of the study together.