In 1800 was Vienna the 4th largest city in Europe?

Apparently not. According to John Merriman's A History of Modern Europe, the ten largest European cities in 1800 were:

1. London - 950,000

2. Paris - 550,000

3. Naples - 430,000

4. (tie) Constantinople - 300,000

4. (tie) Moscow - 300,000

6. St. Petersburg - 270,000

7. Vienna - 230,000

8. Amsterdam - 220,000

9. Lisbon - 180,000

10. Berlin - 170,000