Does an indemnity agreement have to be signed to indemnify the city against unknown and unexpected risks?

Our view is fortified somewhat by the cited case of Bryne v. City of Gloucester, 297 Mass. 156, 8 N.E.2d 170. But there is an important factual departure from this case, for the contract between the indemnitee and the third party involved in the Bryne case was made after the indemnity agreement was executed, whereas it was already in existence in the instant case. However, the Bryne decision does stand for the proposition that an indemnitor is not to be held obligated to protect against unknown and unexpected risks. At page 172 of 8 N.E.2d the court said: 'We think the parties, when they made the original contract, must have intended that the contractor should indemnify the city against the legal consequences which in the light of then existing conditions and from the nature of the work might naturally follow from the contractor's acts, but not against new and unexpected liabilities which the city might voluntarily assume by future agreements without the contractor's consent.'