This task is about reading the given passage and construct a question about the information present in the passage. Construct a question in such a way that (i) it is unambiguous, (ii) it is answerable from the passage, (iii) its answer is unique (iv) its answer is a continuous text span from the paragraph. Avoid creating questions that (i) can be answered correctly without actually understanding the paragraph and (ii) uses same words or phrases given in the passage.
Q: In 1808, Napoleon and Czar Alexander met at the Congress of Erfurt to preserve the Russo-French alliance. The leaders had a friendly personal relationship after their first meeting at Tilsit in 1807. By 1811, however, tensions had increased and Alexander was under pressure from the Russian nobility to break off the alliance. A major strain on the relationship between the two nations became the regular violations of the Continental System by the Russians, which led Napoleon to threaten Alexander with serious consequences if he formed an alliance with Britain.
A:
What meeting did Napoleon and Czar Alexander participate in in 1808?