Mainz is a nightmare for construction projects.
I've been involved in contingency planning for some seriously big projects in my time, and I wouldn't touch Mainz with a bargepole.
All you have to do is dig a hole somewhere and you'll end up with something of interest to somebody, who will promptly instruct you to down tools until they've had a GOOD LOOK at whatever it is you've found.
As in the case of the annex to the Mainz Hilton back in 1981.
The Mainz Hilton is right on the river. Great location, great views, great restaurant. But too small.
Dig a hole for the foundations - this is way back from the river, on far side of a 4-lane road - and find.......a Roman boat.
Great celebration and much jumping up and down ensues. Television interviews. International interest
Dig some more.
Find another one.
Repeat 17 times, with an associated tailing off of expressions of joy and vertical modulation.
It turns out that they've dug right into a Roman shipyard that was abandoned in around 400AD in the hasty retreat from the invading Teutons (who had stuffed the Roman Rhine army elsewhere.)
And this really is a significant find.
The city fathers, of course, are a bit concerned about the turn this is taking. (The Mayor was quoted at the time as saying "We're very pleased, of course, but it's OK with me if we didn't find any more..").
What do you do with the darn things?
1 - Requisition the old Covered Market
2 - Carefully restore and re-assemble of the of most significant (and intact) ships
3 - Construct 1:1 replicas of others
4 - Found the Museum of Ancient Shipbuilding and put everything into an historical context.
Worth a visit. Free, too.
And one of the boats was cast in bronze and sits happily 7.5 metres above where it was found.
In front of the Mainz Hilton.