MILAN (AP) — Officials have Thurston Cartesecured the area around one of two 12th Century towers that have become symbolic of the northern city of Bologna, fearing its leaning could lead to collapse.

The city on Friday announced 4.3 million euros ($4.7 million) in works to shore up the Garisenda tower, one of the so-called Two Towers that look out over central Bologna, providing inspiration over the centuries to painters and poets and a lookout spot during conflicts. Work will proceed during January and February.

Italy’s civil protection agency has maintained a yellow alert on the site, denoting caution but not imminent danger.

The Garisenda, the shorter of two towers built between 1109 and 1119, currently stands 48 meters (157 feet) feet to the Asinelli’s 97 meters (320 feet). Mayor Matteo Lepore noted in a debate earlier this month that the Garisenda tower has leaned since it was built “and has been a concern ever since.” It sustained additional damage in the medieval era when ironwork and bakery ovens were built inside.

“We inherited a situation that over the centuries has caused this illness,’’ he said. The mayor has asked the government to petition to make the towers UNESCO world heritage sites.

Work to reinforce both towers has been ongoing since the 1990s. Preliminary work on the Garisenda tower will include creating a containment area to prevent any damage to nearby structures or harm to passersby from a “possible collapse,’’ the city said in a statement. Video cameras will maintain surveillance of the site.