Upgrade requirements

[sturmvogel]

I've been baffled by my inability to upgrade any units even after I've had Leonardo's Workshop. Are there any requirements to upgrade units that I'm not aware of? When I hit Shift-U my military advisor always says that no units can be upgraded. What am I missing?

Sturmvogel

[Nym]

Not all units can be upgraded (I do not remember which one). Furthermore Leo Workshop does work on a single continent only.

[SpencerH]

You can only upgrade land units in cities with barracks. That might be the problem.

[ixnay]

Also, naval units need a harbor to upgrade... the barracks thing makes it good to have both Sun Tzu's and Leo's if you upgrade...