Rijeka, Croatia ? Despite advancing age and ailments, a determined Pope John Paul II began his landmark 100th pilgrimage on Thursday — a grueling five-day tour of this ex-Yugoslav republic still struggling with the legacy of war.

Blinking in the afternoon sun, the 83-year-old pontiff was helped by aides into a chair atop a cart, and then was wheeled along a red carpet during the welcoming ceremonies.

He immediately spoke of his pilgrimages — including two previous visits to Croatia — that have made him the most traveled pope and kept him on the road for 575 days.

“I thank Almighty God for having allowed me to come back among you on this, my hundredth pastoral visit,” John Paul said. He said he brought a “heartfelt prayer for peace.”

Although his left arm shook and he gulped deep breaths, the pope delivered his arrival speech, in Croatian, in a strong and clear voice. He then boarded a catamaran to cross a bay to Rijeka’s harbor, where thousands of cheering pilgrims gathered to greet him.

Earlier, boarding an Alitalia flight in Rome, John Paul was helped by aides onto the special lift he uses on aircraft. The airline presented the pope with a cake in honor of his trip.

The bell tower, left, and St. Blaise Church, right, are illuminated in the old town of Dubrovnik, southern Croatia. Pope John Paul II is expected to pay a visit to the church today during his five-day visit to Croatia. St. Blaise is the patron saint of sailors and seamen.

John Paul’s trip, which gets into full swing today with a visit to the war-battered southern coastal resort of Dubrovnik, will test anew his ability to deal with Parkinson’s disease and crippling hip and knee ailments.

The pope expressed his affection for Croatia — after his native Poland the most Catholic Slavic country — praising “the ancient Christian roots of this land steeped in the blood of countless martyrs” and referring to the difficulties after a 1991 war for independence from Yugoslavia.

About 80 percent of Croatia’s 4.5 million people are Roman Catholics.

Pope John Paul II waves to the public in Rijeka port, 95 miles southwest of Zagreb, Croatia. John Paul is visiting Croatia for the third time on his 100th overseas trip, today through Monday.