Although set in Rome, this was originally set to be filmed on Bristol. The Burtons' tax advisors decided that Germany had a better tax regime, so the production ended up lensing in Munich.
In an ironic life-imitates-art twist, the real-life marriage of Richard Burton and Dame Elizabeth Taylor was falling apart during the production of this movie. According to on-set reports, the two would rarely speak (and almost never civilly) except when required to film scenes together. The couple divorced in June 1974, then reconciled and re-married in October 1975 - and divorced again after only nine months, in July 1976.
From memory, the production company, Harlech Television (HTV) serving North Wales, one of the great and nowadays almost forgotten ITV networks, reputedly blew its entire drama production budget for that year on this project.